For a bit of freeride/DH riding, there are some jumps and tracks in Belmont woods on Belmont Drive, which is just passed Ashton court heading out to nailsea, but these are only short tracks, more for sessioning.
There is a load of stuff tucked away in the Mendips, it’s great fun, but there is a bit of a ride back up the hill, which is ok on my sx trail but will be much harder on a full DH rig.
Bad asse bikes will point you in the right direction if you pop in.