The British Museum have a free exhibition just now called Light, time, legacy. Running in Room 90, part of the prints and drawing collection, it displays the watercolours Francis Towne painted in Rome and Italy during his tour in 1780 and 1781.
It is always quite surprising to see how empty and overgrown Rome was in the 18th and 19th Centuries : a lot of the monumental stone work was ruined, a lot of the city abandoned by people. Possibly quite a romantic atmosphere for those of a certain temperament however, and Towne's art is extremely good. There are a lot of pictures here as well, and I'll have to visit again.
The Guardian also has a glowing review. It would be a shame not finding a way to permanently show off Towne's beautiful work.
Here are the 113 results of a search for Francis Towne at the British Museum site. Lots of wonderful watercolours to admire.