Monster Mine is a Venture Bounty level in LEGO Dimensions.
Most of Soren Helt's organization ends up in a den of Void Monsters and almost gets killed before Prisco saves them.
Section 01: Abandoned Mine
Use Voldelem's knives to cut through a few Void Monster webs. You'll encounter a few Void Larva, but these are completely harmless (albeit kind of creepy). You can kill these for extra hearts. Eventually, you will enter a cavern with a group of Void Antlions. Finish them off before moving further in the mine. Watch your back as you do, though, as a pair of Acid Spewers start spitting at you from behind. These take a few more hits to kill but shouldn't pose too much of a problem.
As you advance through the grotto, look for little webs on the walls. You can cut open up these webs with Voldelem to get studs. There are more Antlions as you progress through the level. This is the point where most of the party gets taken by Antlions in a cutscene.
Robert and Robyn are not caught with the rest of the group, however.