I don't know if it is too late, but if you haven't already completely finished designing crypt 4 can you put a hard maze in it somewhere?
A very hard and long maze that leads to a lot of dead ends and traps with only 1 entrance and some exits each leading to an item or something (e.g. orbs, hidden treasure chests, etc).
1. For example, the maze can be like say on the 5th floor or something and the trap may drop you down to a previous floor and you have to make your way back up.
2. Or traps lead to fights
3. Or just regular traps that hurt you.
If it takes too much time then nvm.