You need to double back to the hole that you entered. And then you need to go back to the zookeeper's lair, remember where she had the blast door in the reptile exhibit?
Oh also, found a bug. If you go over the tile where Paunch has his problem and you can save him or leave him, it triggers EVERY time (accidentally went too far back, triggered it, went south, went north again, for the third triggering on the same save.)
