...a signal box on the side of the railway line, somewhere in East Sussex - presumably not far from Rye.
A signal box is where the signal man used to manually operate levers and handles so that various pieces of equipment were set in the required position for each train that passed. The raised design also provided the signalman with a good view of the railway under his control. These days, signal changes are managed remotely, so no idea what the signal boxes are used as, but there are several dotted around South East England, and I reckon this is one of the prettiest.
If you're a railway enthusiast, you can read (a lot) more about the Rye signal box here and about signal boxes in general on Wikipedia. Apparently, signal boxes are called signal cabins in Ireland, interlocking towers in the US and postes d'aiguillage (literally "shunting stations") in French.
Never let it be said that blogging isn't educational.