Originally posted by KierraElizabeth ...If you could take *just one* lens on this kind of adventure, what would you take?.
Much depends on who you are as a shooter of course...
From my own gear I'd pick out the Pentax 18-135mm. It's a lot of flexibility in a WR lens. Yes, sometimes I wish I could go a bit wider, but if I'm only taking one and I can't guarantee conditions, that would be the choice. If I didn't own it (or your Sigma 18-135 isn't WR), the newer choice would be the DA 16-85mm, also a WR lens. You might not really need the 135mm reach for general landscape/architecture, but what about wildlife in the landscape, or the occasional candid street shot where you see something down the block? Would missing those shots be acceptable? If so, or you just don't find yourself ever using the telephoto range, then a 12-24mm might make more sense.
If I can take two lenses, then the one in my coat pocket is the Sigma 30mm f/1.4 Art. Not WR, but it comes out at museums and other indoor, low-light situations where f/3.5 won't quite cut it, and I'm not as concerned about conditions. Sometimes with hand-held indoor/evening shots, just being able to trade everything for more light can be important to me.
None of these are exactly tiny lenses of course. If small//light is super-important (Like you're doing this trip out of a carry-on and really want a purse-able choice), I might think seriously about a MILC.
Have a great trip,
traveler
(handle on DPReview is bob5050)