i cant seam to make a tunnel.. it could be because i dont know how.. or what tool i should use..so if someone has a turtorial or just tell me which tool it is for hammer im sure ill figure it out.. thanks..

example: like the tunnel on forest when you go the backway and have to blow up them big rocks to open it up...

making a tunnel would be just the same as making a hallway etc, you'd have you're floor, sides and roof, if you wanted it to be sloped and "rough" looking you could cut alot of it into triangles and use the vertex tool to make your slopes in it.

The walls that are destroyable would be made of func_breakables triggered only for breaking with bazookas etc.