try splitting stuff into bits... like, aerobic, anaerobic, strength, flexibility, power.

aerobic can be done on the bike really well cos you can track your HR etc easily and hit and maintain whatever thresholds you like.

in the gym for strength obviously, or swissballs (or rock-climbing ay benson) etc etc

power in the gym or you can do plyometric stuff, hill-bouncing and other land based running type stuff, probably heaps you could do there...

anaerobic obviously in the water, or you could maybe do some free-diving techniques? that stuff is new to me...

flexibility, yoga etc.

try some circuit training classes in the gym maybe? i always wanted to try some of those... jumping around, doing unco moves, wearing leg warmers, you know.