It wasn't long ago when I was invited to go zorbing for my friends hen party. At the time I had no idea what it was but said that I would go along; little did I know that it would involve being strapped inside a large, plastic ball and being pushed down a hill!
You may, or may not, have heard of zorbing. For those of you that don't know, it basically involves rolling down hill in a large, transparent orb. As you can see from the images, the orb fits two people that are strapped in by velcro sitting opposite each other, with one person going backwards and the other going forward. From my experience it is well worth trying, even if you just have a go the one time. I would also recommend going backwards - far less painful and more enjoyable! It could be quite painful as the orb rolls over bumps in the ground when going forwards, as you are going head first, rather than feet first! But apart from that it really is a great experience.
I think this is a great activity for hens/stags, as it's something a bit different and it's something that everyone will always remember. A lot of Outdoor Centres provide this activity, along with many others such as paint balling, archery, etc.