Adding to that, here's slope soaring, which is really cool. I haven't really done a lot of this due to having to travel far to have access to this type of geography. Beautiful silent flight, no motors required. They do add motors to some of the planes just so you have backup in case you lose lift. Here's an excellent intro to the sport:
https://www.youtube.com/watch?v=Ev5fSVi1PrA
And then there's the absolutely crazy/demented --in a good way-- dynamic slope soaring. I have yet to experience this. This is the domain of sophisticated carbon fiber and top-quality components. You can find videos of planes exploding in flight due to loads.
This is a long video with a detailed technical explanation of dynamic soaring:
https://www.youtube.com/watch?v=nv7-YM4wno8
548 mph (882 kph) run: