This challenge is a great test of patience and determination. It's a lot like Ironman, with a few differences. As with Ironman, you start the game and proceed directly to the Infinite Dungeon. The object of the game from this point on is to get as deep as you can into the Infinite Dungeon. Unlike Ironman, you do not have to leave the level when you see the stairs. You may stay on any level as long as you like, to gain experience, artifacts, or whatever else you like. The only stipulation is this: once you have gone down, you can never go back up. For example, when you go down to level 2, you may never go back up to level one. This challenge requires much more skill and patience, as opposed to the others which require mainly luck.
I don't know if the Infinite Dungeon has a bottom, and I doubt it does, but I do think it would be interesting to see what kind of monsters are at say, level 3000. There may even be new ones we don't know about at very very low levels. Only Herr Biskup knows that. Still, I think it would be a fun thing to do, maybe to incite competition among players as well.