This cache forms part of the 5 Bridges series, a series of 4 caches, all associated with bridges, scattered around NE Cumbria, each containing a clue leading to a bonus cache (GC5H09N). The clue is laminated and attached to the inside of the lid. Our hope is that everyone who completes the series will have discovered at least one new place they haven't been to before (and be happy they did!). Each cache is in a location where there are walking options for those that want to make a trip of it.
This cache is within the Irthing Gorge on the Cumbria/Northumberland border and near to Gilsland Spa, a sulphurous spring which has been a tourist destination since the 18th Century. If you continue the walk beyond the cache then you can also get to the Popping Stone, a famous local landmark that seems to have had associations with courtship rituals and marriage proposals also dating back to the 18th century.
If you glance at an OS map you'll see that the cache can be approached from various routes so you can take your pick, but wear suitable footwear as all routes can be muddy. Probably the easiest is to park at the Gilsland Spa Hotel. If you follow the path signposted Spa Well and Popping Stone you'll come to a bridge (no, that's not the one with the cache!). If you cross the bridge, then take a left through the gate into Woodland Trust land and follow the path you'll come to another bridge and the cache is on the other side. So, two bridges for the price of one! 
You can continue to the popping stone or make a round walk by returning on the path along the W side of the river.
The cache is a lock-and-lock box with a few swaps (and a trackable at time of placement). GPS was bit tricky even in November so could be a problem in summer but the hint should be enough. If you have small kids with you keep an eye on them around the bridges.