You should be standing in the small car park next to the remains of the Roman fort.
Almost 2,000 years ago the fort Melandra (probably known to the Romans at Ardotalia) comprised a wooden barracks, a small bath-house, kitchens, and a principio (operational headquarters). The fort was engineered and built by the 1st Cohort of Frisiavones under the command of Velarius Vitalis and later garrisoned by the Portuguese auxiliary 3rd Cohort of Bracara Augustani. The structure was initially a wooden construction but was rebuilt in stone around 70 CE. The new fort was built in the shape of a rectangle, often described as a ‘playing card’ shap, with watch towers were erected at all four corners of the fort.
The sketch below was undertaken my archaeologist and illustrator, Mike Brown. You are in the area marked ‘MODERN CAR PARK’