Quote Originally Posted by OakLeaf View Post
It's no different from riding in the flatlands ... if there are no elevation changes and no turns, you never change your position on the saddle and it gets uncomfortable pretty quickly.

Lots of LBS's have group trainer/roller sessions in the wintertime, helps break the monotony anyway, and you get to ride your own bike instead of those ill-fitting things they have in the gyms.
I discovered this summer how truly hard it is riding in the flatlands, but at least there is some capacity for coasting and the bike moves around under you to move the pressure points around a little bit.