Two weeks is pushing it for anywhere high as you need to acclimatise. The Annapurna Base Camp is the best short trek in Nepal (from memory you can do it up and back in 5 days but it is quite hard walking). You go from bananas to glacier. The circuit is longer (15 days plus) and they've built a road on the Muktinath section so it can be done faster if you use a vehicle. Tibet is harder to plan logistically and won't be easy to get into at present as it is sensitive anniversary time.
Two weeks is pushing it for anywhere high as you need to acclimatise. The Annapurna Base Camp is the best short trek in Nepal (from memory you can do it up and back in 5 days but it is quite hard walking). You go from bananas to glacier. The circuit is longer (15 days plus) and they've built a road on the Muktinath section so it can be done faster if you use a vehicle. Tibet is harder to plan logistically and won't be easy to get into at present as it is sensitive anniversary time.