Trial Chambers in both Java and Bedrock can generate with cave features, biomes, and other structures inside or intersecting with them. 

This includes but is not limited to:

Glow lichen, vines, amethyst geodes, cave vines, spore blossoms, dripstone, sculk, dungeons, mineshafts, strongholds, ancient cities and bedrock.

To recreate this: 

• create world with 1.21/ next major update experiments on in latest preview or snapshot
• locate and teleport to Trial Chambers structure 
• depending on biome you are in or surrounding structures, they may intersect