So, I've started to develop a short-list and thought I'd present it here to hear if anyone has any recommendations. Without further due, here it is:
1. Mt. Blanc. It's the highest mountain in Europe and a fairly easy, non-technical climb. Maybe too easy, in fact. The mountain is climbed by thousands every summer and the record is a little over 5 hours round-trip from Chamonix. With a bit of acclimization to the high elevations, it could at least prove to be a good 1 day training effort.
2. Mera Peak. This is a 6500m high peak in Nepal. It's one of the highest, non-technical climbs in the Himalayas. This is certainly more challenging than Mt. Blanc, mostly due to the longer trek up the Hinku valley. This climb would most likely take 15-20 days, including the trek up the valley and some time for acclimization.
3. And finally, crossing Greenland on skis. Much more of a flat adventure, but being exposed to the Arctic weather would surly create a challenge. The length is about 600km and would most likely take around 18 days to complete.