I found a way to survive the gamble: when you enter it, go down, at the next spilt-up go up, then down twice. If you did that right, the third door is opened.

To get to the secret warp, you first must find freezer ammo. Go past the pit that tells you not to go on unless you destroyed the Tzarin gem, to that staircase(?). On one of the right walls you'll find a secret. Go as far as you can and stomp the crate with freezer ammo.

The secret teleporter to the layer-3-maze can be found on coordinate 285,255. And again it's hidden; in a floor. With a bit luck you'll find it, shoot a few blocks and freeze the spring. Search on and you'll be warped to coordinate 174,37.

But, why do you get TNT ammo?