On rare occasions, you may notice that trampolines will be facing a different way that normal. That means your about to enter a Rumpus Room. A Rumpus Room is a rare room that has you battle many Pokemon (almost like a Battle Royale, except with money and no boss Pokemon) and let's you obtain a large amount of money.
There are two types of Rumpus Rooms. One type has you face different Pokemon from that level. The other focuses on one evolutionary chain, with four large evolved Pokemon and many little ones.
Here's a visual:
Typical Rumpus Rooms from 1-1Trailhead Field
Rumpus Room Type 1
Rumpus Room Type 2