In reply to maybe_si:
If you're looking for adventure within a three week time-frame, then it'll have to be somewhere with a decent travel infrastructure, otherwise you're going to be spending a third of the trip just in transit. Really, you need 5 weeks as a minimum (the Mick Fowlers of this world can do these things in less time, but the rest of us humans can't).
It's your big trip, you're already hyper about it, make it really memorable by taking a bit more time; living and travel costs in Asia are pretty low, so with a year to save up, a two-month trip oughtn't to break the bank.
As to where to go, well that's an impossible question. For me, if you haven't been before, then Nepal. But we're also looking at a trip down to South America next year, so I'll be following this thread closely. One of those times when a wealth of experience should shine through - and hopefully no mention of BG......