If you haven't done it before, it is a great weekend. Racing up and down the Welsh hills against upto 60 horses (and their riders). Full race distance is 21 miles (ish), but you can enter as a team of three. Each leg has a lovely hill and a river crossing in it.
Accommodation gets booked up (and race sold out very quickly last year) so get yourselves organised. There is camping available near the 'town' centre too.