In the 360 version of Spelunky (not the PC version, which is different) what secret levels are there and how do you get to them?
There are six found so far, but there may be more. I've only found the first four, so credit has to go to Todd Schlickbernd and SnapDragon for the last two.
Real last step:
During Olmec, the final boss,move around until the book writhes at it's face the most. (it starts slow ,then speeds up as you get closer). Defeat Olmec over that spot. There will be a door. This door has no step, so jetpacks or capes make no difference. You must use Olmec's face as a step as he sinks into the lava to get to hell. This is impossible without the book, as the door will not appear if you do not have it.
The worm is much larger than a standard level. In a pool of acid inside is the Crysknife. It one-hit-kills ANYTHING. Be sure to retrieve it. Also, in the green background decoration with a silhouette, whip it to free a secret character.
At the top inside of the haunted castle is a secret character. Whip the coffin to free him.
The mothership is reverse and drops you off at 3-3, although it appears at 3-4. Within are alien lords and the alien queen, whom guards a very destructive plasma cannon.Break open the distinct alien pod in the background to unlock a secret character.
The black market entrance does NOT appear on most levels.Only one chance to enter appears on 2-1, 2-2, or 2-3.