Seriously. Forget all of that gym stuff and take up riding a unicycle. It is way more fun than bicycling, is a cardio workout like no other and builds strength all at the same time.
Unicycling requires continuous pedalling. Without brakes or gears, it is work both up and down hills and your legs go like crazy on the flat. Plus you develop incredible balance and coordination.
The mental focus to keep upright is an excellent meditation too. On the whole it is a very addictive activity.
I've been riding for about eighteen months and do 30 to 40 km a week. I'm nearly 56 and my body shape and strength has never been this good.