Catherine

The Secret Achievement is "A God is Born!"

You have to conquer the final stage of Babel - Axis Mundi.

You unlock this stage by having completed all 9 story chapters on normal or hard with gold prizes (that gives you another achievement).

Play it in coop with two controllers because then the stage is much easier and shorter (about 160 steps).

If you want to have an easy time, you can "cheat". If you have the chance to push away all blocks except of one - do so! Make sure none of the forthcoming blocks have a chance to fix on other blocks than the one you coose. Now just push away everything and just move up one block after the other.

REMEMBER: Somewhere in stage 8 you HAVE to re-create a "broader" road in order to have a chance to reach the goal.

You can see what I mean in this video by minute 23-26.

This player plays solo, in coop the stage will be quite different.

Sorry for my English, I am German ;)

BTW: Thanks for the negative votes - my tactic really works, perhaps you try it for a chance. Nontheless - the stage is not easy even with the trick.

The other solution is good, however I wanted to add a few things and post a video I made to help out a little more.
I think the easiest and best way to do this is with 2 controllers.
I put a pillow on my lap so the controllers didn't slide around and kept at it til I got it.
As you can see in the video, I barely made it.
Watch me panic at 18 minutes or so when I'm on the last row before falling to my death. I managed to turn things around and finish the level. So don't give up even if it looks like you're not going to get it.
Anyway, I try to make each platform as flat as possible with a broad base even if it seems like I'm wasting too much time. This is more important on the later stages of Babel.
Watch what happens when you pull out or push a block out and what the consequences are. For example, when you pull out a block out from the end of a row, if the row above has an unsupported block that sticks out 1 block farther, that block always falls. That's why in the video I posted, I always try not to pull out a block on the end of a row if I can help it. Unless that will help me where it will fall.
Here is a page from the Catherine Wiki site with a lot of great advice on Babel:
http://catherinethegame.wikia.com/wiki/Babel_Tips
Even though it says elsewhere that the blocks are random, they aren't. There are only a finite number of combinations and there are only a relatively few different patterns that come up. You'll notice that the patterns are very similar from game to game. Not exactly the same, but similar.
I got this from the Catherine Wiki page posted below and above.
This page below also has some good info on Babel in general too including approximately how many steps for each babel level in both single and paired modes and a few videos on the single player:
http://catherinethegame.wikia.com/wiki/Babel
There are things to remember in paired mode. Both must survive and don't block your partners path. I know it seems obvious, but it's really easy to do.
Obelisk was the hardest 1 for me to do of the 4 levels of Babel. If you can do this level, the last level is easier IMO.
The key to this is patience and practice, if I can do it, so can you, good luck.

in case anyone else in wondering, this one is broken for solo play in the region 1 release (north america);
playing in pair mode (offline co-op mode) is the only way to get this;
any doubts should be settled by checking the leaderboards, it currently caps at ~90 steps;
also, this will build on all previous techniques, and your main danger will be the black hole blocks, which you can spider around, but not stand on...

I'm just going to add some tips for anyone struggling with this. As always, solo for NA/(EU?) is bugged, so don't try. I've only gotten 40 steps, and the person at #1 on the leaderboards for it got 132, with the goal being... 300. I'll be frank: I think it's probably possible. The block layouts are absolute crap, but I'd wager it's probably possible under perfect circumstances and a lot of code layout diving and absolute mastery of the game, unless otherwise proven. But for the rest of us, it's not going to ever happen. So don't try. Now:

First off, there's no inherent solution to this. Say the first 5 or so rows of blocks are the same as someone in a video you're watching. But then the next 5 are different, and the next 5, and so on and so forth. It's very randomized, but there's a few inherent patterns to it you'll need to watch for.

Namely, there's a "break" area around 90 blocks, and around about 150, you're virtually in the clear unless you manage to mess up in some stupid way. The game gives off a "Halfway there" message at 97 steps, but it's not true, you're probably going to see the objective around 150-160 steps. The hard, hard parts of Axis Mundi are around the 40 mark, and around the 100-140 mark. This is where sheer force of will and cognitive ability come in to play. If you're constantly screwing up around here, that's fine: these are where it's at its most difficult, and it's where you're going to mess up the most.

I would recommend you be at 48/50 achievements when you do this. Rapunzel, Hard Gold prizes, everyone saved, all endings; all of that out of the way. You need a lot of practice, techniques, and patience under your belt. A good stage I could recommend would be something like 7-4 on Hard in the story, for some higher level practice. You need to know how to make footing out of nothing, where it seems impossible to get footing. Watch a video of the 100-140 section of Axis Mundi, you'll see what I mean. Giant, randomized walls with holes everywhere and by that point, even with the leeway you get around 90, the falling stage will be breathing down your neck.

After a lot of practice, determination, and a little bit of luck, you can get this. As of the other day, I'm now the 285th person tracked on TrueAchievements to get it (taking all 3 regions into account). It's not a common achievement to have, and a difficult one to get. Know the game, keep your head, and you can get it too.