I'm an ex-rower in my 40s and my usual cardio workout these days is 10km at about a 2:05 pace. Lately I've been watching Breaking Bad episodes during each workout, it's about the right length and a nice distraction!
Sometimes I do a 5k at about 1:55 instead. Between that and weight training, trying to build back my endurance before doing 2k sprints again. Maybe I'll get back on the water next year.