Rose window. It doesn't look like a sophisticated example of symbolical geometry, it is simply basic. 12 colums radiating from the circular centre and with the cross shape clearly distinguishable. It doesn't look like any other number is put in evidence. The abbey has got a clear structure: cloister, church, dormitory, some other service room. The type of stairs you can find there are interesting: apart from the ubiquitous spiral stairs, there is at least an example of the climbing-on-the-wall type, the same that you can find in the cathedral of Trento (without columns, though). The chapter house has got a fantastic echo.
