My advice: if opportunities are limited get yourself a road bike. You can ride straight from your front door, go out for an hour and come home elated and absolutely beasted; your fitness will rocket into a different level and you won't need to spend ages driving to and from the bike ride then washing all the dirt off the bike and your kit.
I made the change after 21 years as the world's most fanatical mountain biker and the road is so much better and more convenient that I've sold my mountain bike and my cross bike. The cash went towards an Italian hooligan bike, which gives me huge enjoyment and I'm now dramatically fitter and slimmer. Many others have made the same change. I now have a stack of cycling buddies, 14 of them came to the race I staged for my 60th birthday.