I live in the flats, it's 20 miles to the hills and these are just hills not mountains. For the last three weeks I've driven to the hills on Sunday and ridden there. It's about 52 miles with 2000' of climbing. I can feel the difference, I'm noticeably stronger. Problem is I just can't do this every week but I don't want to lose the fitness either.
I commute by bike, just 6 miles one way, and do a 50 mile group ride on Saturday's. I don't have any more time for riding but I can do exercises at home at night. Is there anything I can do at home to get/keep that hill climbing fitness?