If your taking the Buried Relic challenge then be atleast on Lv.55-60. For Wish Cave, don't even bother with it.. If you need to go there then have a pokemon with good attack moves on Lv.1.
Lets see...
I took on Firey Feild when I got there, because I was kind of scared of Silver Trench...99 long floors... ;-;
It was actually easy for me, but I was at level 70 when I went through it.