I did a spartan style race last summer. It was a 10k with 25 obstacles over various terrain including swims and climbs. I consider myself is pretty good physical shape but it was challenging enough to have to dig really deep to complete it.
One of the last obstacles was a drag. It was basically 2x4's with cross slats which held sand bags and you drug it like a litter across sandy loose ground and weeds.
I'm not sure what the bags weighed but it felt like a 800# by the time I got across the finish line.

Yes, but it was a looooong time ago... have they gotten lighter yet?

Did the Firefighter Combat Challange few years back. You had to drag a Rescue Randy dummy to finish. To say I was blown out at the end was an understatement. Full turn out gear and breathing air off a BA. I was happy to finish.

I grew up on a hog farm and have dragged market weight (275lb) dead animals out of barns. That's on level flat concrete so on one hand easier, but truly dead weight which made it harder.

I haven't done it in the context of firearms training like they do at some of the tactical games courses, which I should get to.

It’s definitely an eye opener the first time you do it. We used to do it frequently on my squad just to get the heart rate up before shooting. I started using the sleds at the gym to keep in practice, though it looks easy that damn thing gets you after a few reps of pushing and pulling.