As quoted from Gymboss -

Whether you are at the gym, on the track, in your house, yard, or on the road a HIIT workout can be completed with great success. Any activity can be used for HIIT training, the idea is to go intense for a set amount of time doing any activity you want followed by a recovery period, and repeat as many sets necessary to meet your goals.

Throw boulders around your yard, run on a treadmill, sprint around the track, up a hill, or through your hood. Pound on an old tire with a sledgehammer, throw the old tire as far as you can, as high as you can, against the wall as hard as you can, as many times as you can in 30 seconds then rest 10 seconds. Repeat, Pick up the heaviest thing you can find and walk around with it for 30 seconds then rest and repeat. Lift that 70 lb punching bag up over your head as many times as possible for 30 seconds, then take 20 seconds off, repeat 10 times. Push your car down the driveway for 30 seconds, rest 30 seconds, and then repeat 20 times.

I think you get the point of HIIT training by now!

This morning tried the Step Bench (which killed my shins) but was a hell of a burn. And to my surprise this morning
at my gym, there was several others doing HiiT. Might have a chat with them tomorrow .