How would I detect if terrain is above the player's camera?

I have caves in my game and I'd like to add an echo sound effect to all the sounds in the game when the player is inside of a cave. To do this, I want to detect if the player's camera is under terrain. Not parts, Roblox terrain. I have no idea where to start since Roblox terrain has no Position property.

Thanks for viewing my question, any and all help is greatly appreciated!

Use RayCasting. You can for example cast a ray upwards from camera position. If it hits terrain, it is probably inside the cave.

https://developer.roblox.com/en-us/articles/Raycasting