There are some things I have to say first. This is not the COMPLETE work. Just for some places might be not noticed or searched for.(except the Souvenir and Secret Constellation)
I totally suggest that you must remember the all places of Souvenir/Secret Constellation first. That will be effective for your journey.
有些事情我必須先說明，這並不是一個完整的秘密房間探索攻略，只是用來提醒一些不常被注意或搜尋的地方(攻略內也除外那12項物品和所有隱藏星星的位置)
我完全建議你必須先熟記所有12項物品和隱藏星星的位置，這將對你的旅程有所幫助。

If you were not, just take a look. 如果你沒記熟，那麼看一下這個網址。
Souvenir/Secret Constellation Guide - Macuelos
All you need is the trick actions to get the targets. 你所需要的是技巧性的方式來達到目的地。

There is a trick skill I use often:
When you fall down in air, use a beam on the vertical wall to make Kurl floating.
I use this skill to search for some places like two vertical walls side by side. It's useful.
這裡有個我常用的技巧:
當你在空中處於掉落狀態時，在最近的牆上丟一道光束來使自己飄浮。
我常用這個技巧來探索一些並列且垂直的牆壁，這很有用的。

You can get this achivement in easy/Normal/Hard mode.
你能以任何難度來取得這項成就。

Before get the Cube, here is a man, just walk through.
在拿到隱藏星星CUBE前，這裡有個人，只管走過他身邊。

Jump in. 跳進去就對了。

Here is one. 這裡也有一處，位在隱藏星星的底下。

[7/31/2014]Provider: @Ancient Dog
There is a up-down platform (with needle) . Place a beam on that and float up. you'll see it.
有一個上下移動的針刺平台，在上頭使用光束然後飄上去即可看到。

[7/27/2014] provider: @rod
http://i1.minus.com/i1d3P489kcHSR.jpg
When you enter Dining room , don't forget to jump up here. [Image Missing]
在第一次進到Dining Room時，別忘記跳上這裡。


[11/14/2015] Provider: Hibou
http://cs2bus.com/sharedfiles/filedetails/?id=553922481
At the very first place.
應該是在剛進到這區域的地方(太久沒開了)

Use a bomb to get in. 使用炸彈來炸開裂縫石。

Before get in the Hub, this place is hidden by screen.
在進入中心前，這處地方被螢幕擋住了。


Sitting room Hub
I took these with Macuelos's guide. So you can follow the order of the guide to get these places.
我在進行這部分時和Macuelos的攻略一起進行，因此你能一邊看他的攻略順序一邊對照我的。

South 南邊
Cross that floating platform. And use beam on the ground.
越過浮動平台後，在地上放置一道光束。

After that, not to get far way. Use beams on that spikes. Until floating up that height, go left.
在那之後不用走太遠，在那些針刺上放置光束，之後跳上去，飄浮到如圖的高度時向左走。

Before you fight the mini boss, make use of the platform beside wall.
在你對決小BOSS前，利用一下靠在牆邊的限時平台。


West 西邊
Use some trick way to get in. Or stand on the left side and jump down carefully.
利用一些技巧性的方法進去，或是站在左邊的平台然後小心地跳下。

Tiny passage. 狹小的通道。

North 北邊
[5/25/2020] Provider: TheStreetcleaner
It's in the North area of the Sitting Room Hub, just after the part with floorchaser.

Before you make your way down to the right, use a Gravity Well on the left edge of the platform with door and floorchaser on it. As you float up through the vertical passage, you'll see a small nook to the right containing about six stars and one blue bomb.

Can be found between 5:44 to 5:56 in this video:
https://youtu.be/ITDF_laDJk4

Near the start place. Jump down for it.
在靠近開始的地方，跳下來取得。

East 東邊
When you see some platforms, you can use wall-jumping to get here.
在你開始看見一些平台時，你可以使用三角跳躍(XD)來到達此處。

Near the mini boss, this place filled with spikes. Get the left side to meet these items.
在接近小Boss前的這個地方充斥著尖刺，到達最左邊來取得這些物品。

[5/25/2020] Provider: TheStreetcleaner
It's about halfway through the area when you first get to the cloudy areas. It's hidden by the clouds at the bottom of the screen and is accessible via a cloud block bridge underneath the main path. There are some stars and a 2 blue bomb pickup.

At 6:05 to 6:19 in this video: (same playlist as my last comment):
https://youtu.be/IAkYgtitE4k

Before you end this area, you can find a secret place in the room which filled with springs.
在你離開這個區域前，你能在這個充滿彈簧的房間內找到一處秘密的空間。

After Boss

This area have some pieces of secret places. I even don't know whether it's counted by system.
So please pay attention to these places for sure.
這個區域有一些零碎的隱藏區域，我甚至不知道那是否有被系統計算進去。
所以請注意並探索這些區域。

Near the end way, this store is in the chimney.
接近結尾屋頂處時，這個商店位於某個大煙囪內。

This area is wide a lot.
這個區域非常大。

Under the bridge 橋下區域
Use bombs. 使用炸彈。

Throw a beam on the conveyer belt and jump on it. Or you can just jump from the small platform.
在輸送帶上丟一道光束然後跳上去，或是你可以直接從那個小踏台跳進去。

South of the Hub 中心南部
If you jump down from Hub. Then get left to start searching these places.
如果你是從中心處向下跳，那麼向左邊走來開始探索。

Make the platform turn to left and jump in.
將踏台轉左並跳入空間。

You must throw one beam on the door, then throw another on the place like the screenshot did.
你必須在門上丟一道光束，然後丟第二個到如圖中的位置。

Up to the springs place. Turn left.
向上來到彈簧區左轉。

Right passage is connect to the "Under the bridge".
右邊的區域連接著橋下區域。

When you fall down here. You can see this place. Now you can get in.
當你從上面掉落時，你能看見這個地方，現在你能夠進去了。

Northwest of the Hub 中心西北部
After kick an enemy and get in.
在解決一個敵人後進入。

You must know here to get the secret constellation. (Also can use Burst Beam for speed)
你必須知道這裡是用來拿取隱藏星星的地方，或是使用Burst Beam來增加取得速度。

Northeast of the Hub 中心東北部
Place a beam on the ground and you'll see it.
放置一道光束在地面上你就可以看到了。

Before get down, walk into the secret passage.
在下去之前，向右走入隱藏通道。

Pass the lights.
通過這些監視燈光。

Hub 中心
This place is near the Northeast area. 這個地方很靠近東北部區域。

[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311072609/1052534326A8E5464F84210181D42923223E6271/
His tip: This place is very hard to reach and I found no tip on the web about this. After 45 min, I managed to reach the little cloud block at the right (the secret is to shoot a gemme DIAGONALLY near the block, not horizontally) and jump to the left.
這地方非常難到達而且我發現網路上沒有任何方法應付這個，在45分鐘後我找出了先到達右邊的灰色小方塊然後向左一個接一個跳。（這個祕密需要丟一束斜角光束在那方塊的附近）

[11/14/2015] Provider: willyzyz
http://images.akamai.steamusercontent.com/ugc/442828190749268030/A278C6C90B1D2DA35BE1E235471EA876801035D7/

[11/14/2015] Provider: RAWЯ
http://images.akamai.steamusercontent.com/ugc/634231172252336225/64F40C6E9C017AFBB3ED7EB09B3C162C5FCF55F5/

When you see the store, you'll find it.
當你看到商店時，你就會找到了。

[5/26/2020] Provider: @TheStreetcleaner
There are a few off-screen areas in the Catacombs that I'm not sure are counted as secret areas, but they do contain some stars and pickups.

1. At 8:08 - 8:18: about halfway through the second area, near the bottom of the gorge/pit. Contains some stars and a 1 life vest pick-up

2. At 10:34 - 11:56: a little after the beginning of the third area, just above the main path you take through the moths. Beam up to the vertical platform above, and either burst beam up to the right onto the cloud block whilst threading through the moths, or alternatively just destroy them and then burst beam your way up as per usual. Contains stars, a 3 burst beam pick-up, a 3 bomb pick-up and a 3 life vest pick-up
https://youtu.be/v0yZ_f1cPsM

3. At 13:17 - 13:51: about halfway through the third area, you will reach a stone pillar with a carving of a frog climbing it, which is beneath two giant stone pillars hanging down from the ceiling. Use your burst beam on the platform to burst up to the cloud blocks above you. Avoid the pesky cloud block enemies above them and make your way to the stars and 3 burst beam pick-up above you using basic gravity beams.
https://youtu.be/v0yZ_f1cPsM

This is in the first area which have many winged enemies. Near the end, there is a small gap on the bottom of the screen.
這位在有很多翅膀敵人的第一個區域內，接近結尾時，有個小缺口在靠近視窗底部的地方。

[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311073230/D8E77F232B4E1BF843090B6078F1F83FADD8D7ED/
His tip: In the Catacombs, in the end of the area just before when we must ride a blue flying "animal" .

[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311073518/7DBB4CB533C86B7A8C17486C28688A0BE14EEF11/
http://images.akamai.steamusercontent.com/ugc/38621479311073794/EB09111602D0F695123AFF4FA58017B9C6A2C6CD/
His tip: In the area with the "animal" : the high/left corner, and the bottom/right corner. Two white constellations that could be secret places because of their locations a little hiden.

There are something you must know...
有些事情你必須知道...

When I got the Mask Constellation, My Achivement is approached.
So, if you were like me, you may get the same situation similar to me.
當我拿到面具的隱藏星星後，我的成就便完成了。
所以如果你跟我一樣，你應該也會有相似的狀況。

If you didn't, Here are some extra places for you. And many places are provided from other players.
如果你沒有，這裡有一些額外的區域，網路上也有其他玩家提供更多區域。

In the final area, use the key to open it. (Must throw a beam on the ground first.)
在後台區域的最後，用鑰匙來打開這個門。

[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311074360/BFB35EFB06EF3B3AC8FFBB08FDB1B6FF1F83B9C1/
As the former place.

In the same area. Near the end of Backstage Areas.
同上區域，在接近後台區域結尾的地方。

After get out of the opera house, to the end of road. Throw a beam on the block and jump down.
在離開歌劇院後來到路的末端，丟一道光束到方塊上然後跳下。

Also you can keep pass the areas to get more secret rooms.
On the moonbase, there are at least 6 secret places.
或是你能繼續通過這些區域來探索更多的祕密房間，在月球基地上至少有6個祕密地點。

The Moon
[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311076318/FC0432A251DCF3EFCB1081E20E8A1B8887F7A5C3/
His tip: (second area I think, but not 100% sure, too much chaos in this zone :-D ). At the end of the zone, a big moon beam put you to a little cave, above the exit.

[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311076970/4C65E308CEC84FED1F11BE2021F026667EC7597D/
http://images.akamai.steamusercontent.com/ugc/38621479311076655/BBBE636C841497219AA20799451DB7C398865BF9/
His tip: The Moon, top of the fortress. When you get out from the spaceship, use a burst beam near its back engine. You will bounce and fly on the left until this little meteor

[5/27/2020] Provider: @TheStreetcleaner
1. At 12:00 - 12:18, in the very beginning of the SECOND main Moon area, just outside the exit to the first laser puzzle, use the Moon's blue burst directly below the ledge to fling yourself onto the nearby small asteroid. From there, jump onto the large asteroid on the right to it when it floats high enough. Once you are on top of this large asteroid, use a basic Gravity Beam to float your way up to the stars, 4 laser beam pick-up, 4 burst beam pick-up and most importantly, an Anti-Gravity Boot UPGRADE/+.

https://youtu.be/ZYqPp36YJxc

2. At 15:38 - 16:17, when you have to cross the chasm in the THIRD/LAST Moon area, use a Gravity Beam at the edge of the right side to float on top of the asteroid that is periodically shooting blue Moon bursts and floating above the slightly smaller asteroid you likely used to cross. Once on top, beam your up to a much smaller asteroid floating just above the screen. From here, there are two tiny asteroid floating high above you: one to the left and one to the right. Use a burst beam to get to either of them. The left contains some stars and the right contains stars, a 2 Burst Beam pick-up, a 4 Laser pick-up and a 2 Anti-Gravity Boots pick-up.

https://youtu.be/ZYqPp36YJxc

Moon Fortress #1
[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311077926/34CEFA569029331AEC62A127098303B00CEE5C95/

Moon Fortress #2 (very hard to reach --> I didn't manage XD)
[4/26/2015] Provider: @Kaiser Panda
http://images.akamai.steamusercontent.com/ugc/38621479311078214/26FC486BE0FE2B8E3406601F0B13BE72A7E4FAFE/

Moon Fortress #3
[5/27/2020] Provider: @TheStreetcleaner
At 15:46 - 16:15, at the end of the 3rd last level of the fortress (Bryce's battle area counts as the last), after running past a corridor of laser bots floating after you, you must jump down into a pit with spikes in it, float your way to the left between the spiked floor and ceiling and then drop down a large vertical shaft that has spiked walls opening and closing. At the end of the corridor when you reach the pit, throw a beam down near the left wall and float your way up and to the left. You will bypass a fake wall and wind up in the secret area: a small rectangular room above the spikes containing a 2 Musical Box pick-up, a 2 Smoke Bomb pick-up, a 3 Bomb pick-up and a 3 Laser pick-up.

https://youtu.be/aI0psuxwds0

Hope you guys also get the achivement. Have fun. Most important of all, I appreciated people who provided secret places. Thank you everyone.
希望你們也能拿到成就，預祝玩得愉快，最重要的是，那些提供更多隱藏區域的網友們，謝謝你們