The highest level bats in the zone are behind the gold door as well as a few behind the ornamental door.
In order to open the ornamental door you need a norg shell and either (3 mythril beastcoins or 1 gold beastcoin, one is done the first time (i think the mythril) and gold every time after that). Talk to the NPC near where Charybdis pops (behind gold door, way to the south) then talk to the npc behind the silver door, trade him the norg shell and coinage he asks, he will trade you a key (rare/ex, breaks on use). Trade this to the ornamental door and it will open briefly as well as breaking your key.