Poltross Burn Milecastle

Milecastle 48, is a milecastle on Hadrian's Wall. Its remains lie near the village of Gilsland in Cumbria where it was historically known as "The King's Stables", owing to the well-preserved interior walls. Unusually a substantial section of stone stairs has survived within the milecastle. The two turrets associated with this milecastle have also survived as above-ground masonry.

Source: Wikipedia