I left the wishing well until late in the game, to get the most effect from the wish (the higher level you are, the more experience it gives you to get to the next level). However, by then I didn't really need the boost.
You could also just start exploring the Dark Forest.
If you get a few strong monsters together, you can kill them, then Resurrect them, run or teleport away so they turn hostile, return and kill them again. Easy but monotonous.
