I've seen a few churches in my life and this one seems pretty unique to me. I did some research on this monastery because it seems so unusual to me (from an architectural point of view) but found relatively little information in my Google searches. Evidently it started out as a wooden chapel built around 1389 and then, in 1393, Pope Clement VII granted the Celestines the authorization to build their monastery there. In 1395 the first stone was laid and construction continued until 1424, when work was stopped due to "insufficient resources". The architect, or Master of Works, was a fellow named Pierre Morel. Anyway, by the 17th century,the "Couvent des Célestins" was one of the most sumptuous in Avignon, with one of the richest accumulations of art. Most of that bit of history comes from this website on Avignon.
But what interested me from an architectural perspective I never found. There are arches that were started but just end in space. The arched window in the upper left corner looks like something Louis Kahn would do - it's very modern. There are capitals to columns that are unlike any I have ever seen. If anyone comes across this blog entry and knows where I can learn more about the architectural treatment of this building, please do leave a comment or email me. I'd love to know more about it.
These watercolor sketches are in my 5x8 handbook.