Many will know the Glen but probably not by its name. The Glen is the field area behind BRGS and Waterfoot Primary School. You can get here by continuing up to the Higher Astroturf, following the path alongside it until you get to some field with a long jump track and sandpit. From here you should be able to spot a gate and you should go through it. That's it, you're free!
There are a plethora of strange things within the Glen, this includes a lot of large rocks, a graveyard, a crumbling wall that leads nowhere, a fenced off pond, and lots of new tree plantations.
Despite the low number of students that venture up here for stick fights or picnics, there are still Welfare Staff or SLT roaming the land in hope of catching you out. If you are indeed spotted, my best advice is to simply say "Oh I didn't realise we weren't allowed here, sorry." And most days the teachers themselves are unsure and let you off with a simple "Well, I'm not actually sure if you're allowed here or not... ermm..." and then leave you to your own devices.
Be careful when coming down the slope again as if you pass the Lower Astroturf you may be glimpsed by yet another patrol of staff members, although they normally just ignore you. The top of Glen Road also offers a number of escape routes and therefore you can just run off.