One-handed kettlebell swing.

For such a simple exercise, this is certainly a lot more fun than it probably should be.
One-handed kettlebell swing
Start by bending at the hips, bend knees and let your right hand hang down between them (as if you’re about to do a pull-through); holding the kettlebell a few inches off the ground. Swing the bell back and forward a bit, and on the second or third swing explosively straighten the hips and lift the arm to above shoulder height (keeping hold of the bell). Lower the bell in the same arc, and repeat.
The idea is to keep hold of the bell at all times, but it’s definitely one for outdoors just in case.
Variations
Most variations increase or decrease the amount of grip work involved. To make things easier, just use two hands or a lighter bell. If you’re looking for a challenge, lubricate the handle with a bit of soap or wrap the bell in a strong towel (grab the towel, not the bell in this case).
Further thoughts
The first time I tried this, I was almost doing a front raise and could really only feel it in my shoulders (as expected). By increasing the hip action, the bell moved higher and there was a lot more lower back work. The amount of work suggested it’d be a good exercise to follow something that hits the lower back more intensely such as deadlifting or a heavy set of good mornings.
It’d also be great as part of a warmup for squats or deads, as it’s primarily a hip movement.