Cupla Resident's Notre Dame Cathedral is a masterpiece, and as he claims, probably the largest (and one of the best designed) Gothic cathedrals in Second Life. Notre Dame makes use of three dimensional features as well as textures, and has a well designed interior. The grounds and setting are very attractive.
I actually found Notre Dame Cathedral reminiscent of the Gothic cathedral in Chartres France more than the famous Notre Dame cathedral in Paris. I think this has to do more with the non-urban setting of the build. The Cathedral is bookable for weddings and other events.
Highly recommended for a visit.