Something a little more extreme, try Friston Forest!

Friston Forest offers an infinite number of waymarked routes for visitors to explore the beech woods. Its undulating terrain makes it popular with walkers and mountain bikers. Both are served with waymarked trails of varying lengths. Mountain bikers have been enjoying the forest for decades. There are trails for all levels of riders, including families. We also have facilities to wash and store equipment.

https://www.forestryengland.uk/friston-forest
https://www.trailforks.com/region/friston-forest/