In today's news, I decided to take advantage of the current lovely weather in southern England, and have a day out combining a trip to the coast, lots of history, and some hill-climbing. The chosen destination was Dover Castle. It's a historical palimpsest - perhaps more so than any other single historical site I can think of. It started as an Iron Age fort; the Romans added a lighthouse (still standing) and the Anglo-Saxons a church (reconstructed by the Victorians). The Normans added some typical fortifications, and Henry II and successors built a great square keep and surrounding walls. After that were further periods of construction and reconstruction, corresponding to the defensive needs of successive eras of warfare, right up to the Second World War.
I last visited in 1990, when parts of the site were still (!) in military use; I think the final military withdrawal was only in 2014. I can highly recommend it: the views all around are impressive, and the history is fascinating.
Oh, and the hill climbing: Dover town centre is almost at sea level; the castle is on a hill-top at well over 100m above sea level, and the tour of the keep involves a climb up to the roof, which must be another 20m further. Lots of unaccustomed exercise for this fenland dweller!