There's always the 14 Peaks - all 14 peaks in Snowdonia above 3000 ft, in 24 hours.
One route is to start at Pen-Y-Pass, then Crib Goch, Crib y Ddysgl, Snowdon, down through Derlwyn and across the A4086, up Elidir Fawr, then Y Garn, through the Devil's Kitchen, the Glyders and Tryfan, around Llyn Ogwen and across the A5, up Pen Yr Ole Wen, along the ridge to Cardnedd Dafydd and Carnedd Llewellyn; from there, you head out along the spur to Yr Elen, then back to Carnedd Llewellyn, and then carry along the ridge to Foel Grach, Garnedd Uchaf, Foel Fras (that's the 14 done) and down over the Drum towards Abergwyngregyn, where you meet up with a road and can arrange a pick up (there's a taxi available that does pick ups all night).
It can be done in 24 hours; alternatively, take three or four days over it, if you have the time.
smithie