Very weather dependent: lots of claggy mud, also depends on what kind of riding you want: not much in the way of waymarked rides though (may have changed in the 13yrs since I left).
Link up Through Whitley/Neston/Rudloe over to Box Woods.
Rudloe round Slaughterford (mudfest) to Biddestone.
Westbury White Horse.
Longleat Estate round Centre Parcs – name of the place escapes me for the moment.
Via Bromham or Sells Green to get up on to Roundway Down, can even go across to Cherhill, Avebury, Ridgeway if you’re up for long distances, or drive to Avebury and there’s a relatively straight forward loop from there along the Ridgeway, Barbury Castle and back across Fyfield Down. Silbury Hill and West Kennet Long Barrow for bonus UFO sightings and prehistoric crypts.
There was always talk of some trails on the hills between Bradford on Avon and Bath, again the name escapes me and I never got round to exploring that area.