The lakes region of the Charles, which is the stretch of river between Newton and Waltham.

I've also done a little urban kayaking in the Charles River basin within the city proper (a little up-river from the Esplanade).

I've also kayaked Beverly Harbor up on the North Shore in (get this) a sit-on-top kayak which is nuts.

At least you don't actually have to feed the kayaks, so that makes my sport cheaper than yours at least. :-)

I know someone who rides horses, so yeah, I hear that horseback riding ain't called the sport of Kings for nothing.