It has been a while since I've played this one, but I think that there is
spoiler:only one spider tunnel, which has two exits. When you leave the crypt where you got the crowbar, there is a turnoff to the left which doesn't look like it goes anywhere but it leads to the hole in the ceiling. You can drop down out of that hole to the main area. If you miss that turn and continue straight, then there is the area with the spider. Past the spider the tunnel continues and that leads back to the crypts, exiting at floor level instead of the ceiling.
spoiler:If you succeed in getting up into the ceiling tunnel, it only leads back to where you have been.