50mm lens is a nice "portrait tele" on your 60D. It's not an indoor architecture lens. The 28/1.8 is a "normal", but also not really in indoor architecture lens. I have and use both the 50/1.4 and the 28/1.8... They are very good lenses... But neither is what I'd be likely to pull out of my camera bag for the purposes you describe.
So, I agree, get an ultrawide.... which for a crop camera largely means get an UWA zoom (there are few primes that are very wide on a crop camera). On a trip, it's generally best to take minimal gear that offers maximum versatility and that often means a zoom.The best low light/available light choice is probably the Tokina 11-16/2.8. However, note the very limited range of focal lengths. It's also a bit more prone to flare than some of the other UWA zooms. These are trade-offs to get f2.8, and frankly I think you might be surprised how seldom you actually need f2.8.
The Canon 10-22 is great in most respects, high IQ and unusually flare resistant... but also one of the most expensive and doesn't feel as sturdy as some of the third party lenses (it's more plasticky... though I have to note this doesn't mean it's actually any less durable... just that it doesn't inspire as much confidence). It's also a variable aperture lens and not particularlly fast (f3.5-5.6).
But, again... f2.8 actually is pretty rarely needed with an UWA... you'll find an UWA handholdable at much lower shutter speeds than usual and often will end up stopping down for sufficient depth of field anyway.
There are also the Sigma 10-20, two versions.... A more affordable one with a variable aperture and a more expensive one with f3.5. And Sigma offers the widest lens available other than a fisheye: 8-16mm. Tamron offers a 10-24mm that has the widest range of focal lengths in a single UWA zoom. I found the Tammy and an earlier version of the cheaper Siggy 10-20 to offer a bit lower IQ overall than the Canon and Tokinas. I haven't compared the others. I do note that the Siggy 8-16mm has a lot of inherent wide angle distortion, not suprising on such a wide lens.
If you are into landscape shooting, you'll probably learn to love any UWA zoom you get for that, too.