How do I detect that someone touched/collided with terrain?

I am messing with smooth terrain and am thinking about changing audio for the material that the person is on or maybe having particles or even just in water making the player anchored then having an ice block appear around them and kill them.

I of course know the classic .Touched:connect(function(hit), but I don't think it is related to terrain bcuz whenever u look for hit it is a part.