In the past horse racing took place in Armagh City on the Mall. However Horse racing still takes place in this location, Farmacaffley. Note the double gates as you drive along the road. The horses cross the road at two points as part of the circuit and the wider gap is required. For most of the year the location returns to farmland.
http://www.farminglife.com/equestrian/plenty-of-excitement-for-large-crowd-at-tynan-armagh-races-1-5900965
The cache is a cylindrical container inside and parking is beside it on the roadside.