Not TOO far from you - the Brecons in South Wales. There are a number of Youth Hostels, and Capel-Y-Ffin is a really good place to stay. Unfortunately the YHA has decided to close it, but I believe it will still be there at Easter (if you can get in of course).
An absolutely superb two day walk is to start at Abergavenny and walk north to Capel-Y-Ffin, and then back to Crickhowell (which is only a few miles from your start point so you can get a bus back). Follow the route of the Cambrian Way for a highly unforgettable two days (hoping the weather is OK of course). I've done it and loved it.
S.