Thwomp Volcano, in the game Mario & Luigi: Partners in Time. Predictably, inside the caverns there are a lot of Thwomps.
In the game, after Bowser kidnaps Princess Peach (who is actually Princess Shroob), Bowser accidentally falls in a Time Hole and appears on Thwomp Volcano, where he jumps inside the volcano and appears in Thwomp Caverns. Baby Bowser also falls here after getting blasted out of Yoshi's Island.
Baby Bowser and Bowser start fighting while Mario, Luigi, Baby Mario and Baby Luigi climb Thwomp Volcano and jump inside it to get to Thwomp Caverns. After a while the Mario Brothers reach Bowser and Baby Bowser, and it seems like they have stopped fighting and became good friends. A boss battle starts, and after Mario and Company defeat Bowser and his baby counterpart, and are about to save Peach, the Shroob Mother Ship comes and sucks Mario, Luigi, the babies and Peach in, and the U.F.O. leaves.
The Thwomp Caverns have lava inside and it erupts every year. Many Thwomps like seeing the lava erupt, most notably Mr. Thwomp and Mrs. Thwomp. However, once Mario, Luigi, and the babies, came here, they stopped the volcano from erupting thanks to E. Gadd's help.