Abel Gance's 1927 silent epic, "Napoleon" - all 333 minutes of it! I haven't made up my mind yet. Don't know if I have the stamina. The easy option would be to get the Blu and watch it in bits. It's a film I have waited 39 years to see. Now I have the chance, but I may just crap out.

The triptych finale (three screens, like the later Cinerama):
