The one I went on was around 4 hours in the saddle. Walk, trot and then some canter and then some full on gallop as well.
There were a lot of riders, I don't know how many exactly but somewhere well over 100 probably. We were split up into groups for the cantering with around 20 or so in each group to keep things more under control.
The views were fantastic and there were a lot of people watching and cheering us on. Towards the end we went onto a race course and went for full gallop. It was so much fun. I'd never before raced full on like that for that long. The horse I was on (a lesson horse, I don't have a horse of my own) wasn't a particularly fast one but he got me through the ride just fine and went for it on the gallop.
I'm really sore and tired now but happy and I'll definitely do it again next year. But yeah.. walking might be an issue tomorrow, I rarely ride for more than an hour so 4 hours fairly full on is quite a lot for me.
This photo is NOT from the riding I was just on but it sort of shows what it's like, in places anyway