Throwing in a rival team of adventurers is a time-honored tradition. Here are a few tables, the first in case I want to let the dice decide the presence of a rival team or not:

And then a few more for inspiration about each type of other teams in the dungeon looking for treasure and glory.

Had to throw in the possibility of a Bastion Free Library Outreach and Excavation team being in the mix. If I was in the mood to let dice decide everything, I might roll to see if the City Councilor from a district in Bastion is with their bodyguards or if they sent their team in without them; seems more interesting for the councilor to be there.

Tunnel Dogs is a term I read in a book about New York City history; they are the city employees who dig do upkeep in the subway tunnels.