Hi! I’m super new to using Syrinscape in my adventures, but I’m having fun so far!
I’m looking for a oneshot sound that’s a huge echoing boom, like something gigantic trying to pound it’s way out of a stone room or prison cell. I have a subscription so it can be from any set.
Any good suggestions?
Have a search for “Tower Booms” in OneShots. Can you find that?
I reckon that might be perfect for you. 
Also [lotr] Doom, doom [lotr] 
Couple of possibilities:
Sci-Fi Player - Sub-Terra - Boom Hit
Fantasy Player - Dungeon Depths - Smashing a wooden door
Sci-Fi Player - The Devourer - Large Explosion (my personal favorite for your request)
I ended up going with Boom Hit. Thanks for all the suggestions!!