I don't have UC, but do have my own health problems. I just spotted this and wanted to say that in August I went to Barcelona. It is a HUGE city with loads to see and do, but it was exhausting. In 1 day, we managed a quater of the city, and only about 30 minutes was walking, we resorted to the tour buses in the end as it was very easy to get lost. The map itself was so big, it was hard to pinpoint exactly where you were.
I suffer with mobility problems though, so this could have been the reason why I found the walk round so difficult and daunting. I have a bladder of steel though, so only needed the toilet once all day and we were in the art museum at that point, so it was easy to find.
I will say it is a beautiful city though, full to brim with things to do and sights to see.
Hope this helps