Town Gate in Óbidos

You're standing at the Castle of Óbidos, tucked into the northwest corner of a walled hilltop town. Start with the walls. They run for more than a kilometre and a half around the whole town, and in places they rise thirteen metres high. They follow the rocks and slopes, studded with square and round towers and battlements all along the top. The castle itself sits seventy-nine metres above sea level.