Rated as 5 stars by TripAdvisor, this is a fantastic day out up in North Wales.
I've done the Ultimate Zip trip twice and the Ultimate Extreme trip once (you can arrange a private trip if you have 8+ people) and every time has been excellent and pushes people to their mental limits climbing high above open chasms and navigating by just your head torches.
This trip advertised isn't as tough as the above but that makes it accessible for younger age groups (see Go Below website for info). If there was 8 of you then you could also have a private trip.
Would thoroughly recommend this as a day out. The temperature in the mine stays the same throughout the year so you'll be fine in Winter.
Note this is not to be confused with the nearby Bounce Below attraction.
£109.50 for four tickets, plus 8% cash back on quidco or 7.5 on tcb