Some of the best riding in Wales around Machynlleth (http://www.dyfimountainbiking.org.uk/) or Coed Y Brenin (http://www.mbwales.com/coed_y_brenin/index.htm).
Hire bikes at the Holey Trail bike shop in Machynlleth or the cyb visitor centre. Great walks and opportunities for climbing in the lovely and less crowded southern end of Snowdonia.
Staying in Solihull's hut nr Cwm Cywarch