[ludicast]

I believe the course list has plenty that do match what the OP is looking for. For example there are several on real analysis, graduate-level optimization and other subjects like that. As well as much easier subjects.

Don't know the OP's exact level or prereqs (he mentioned in another post he had a rough go with both apostol & spivak) but there seem to be several classes that would match his needs/curiousities. The classes might not be at your particular level, but since mixing/matching seems possible I think it would cover a lot of ground.