I was actually about to post about there not being enough spiders...
Odd, me too.
SpoilerShow
I'm on level 7 and combat is super easy (on normal) never died in combat so far. (so far got 2 dead people, but the crystal is very close and it was easy to recover).
When I saw "Mage entrance" I fired a fireball at the statue and that closed the gap. I would guess any mage missle will work, since players can go any magic skill not just fire.
SpoilerShow
You find runes for fireball spell in the next room