Thanks voluntario I got it. It turns out down the bottom of the slope was a set of the doors you just run into to get through, they looked kind of broken, I guess I'm too used to broken looking doors in games being unopenable

Heres a new one for you though, how do I detonate c4 after I've planted it, I guess pressing left mouse must have seemed too easy and hassle free so they had to complicate things?