Chesters military fort is an excellent example of an accessible fort, making use of the natural resources (the river), taking you back in time to experience the Roman way of doing things, with a fine museum as well as the outdoor site. It's only a 25 minute drive from Newcastle, which makes it easy to get to for any day-tripper in the area.
Hadrian's Wall itself was built from 122AD, but this fort, originally known as Cilurnum, was added in 124AD.
The present state of the site owes much to one man, John Clayton, whose enthusiasm for Hadrian's Wall led to immense excavation and preservation efforts. His father bought the Chesters site, and John excavated it from the 1830s. He built up a personal collection of Roman-linked items which is now on view as the Clayton Collection at Chesters. He collected an especially good set of stone altars from around the wall, reminding us how much religion played an integral part in Roman life. It's worth visiting just for the museum, but the site is also amazing.
The site is split into sets of barracks for the men, a commander's more comfortable house, and a distinct bath house. One notable feature is a small strong room, half buried, with its arched roof clearly visible. You can walk down to investigate it further. As you approach, the whole site lies out before you as an extended floor plan.
The barracks flow out in regimented rows, each small room designed to accommodate up to eight men. This was not an environment for women and children, but separate settlements, known as a vicus, grew up around military forts like this one, in order to house the soldiers' growing entourages.
Down by the river is a bath house, perfectly positioned to make use of the natural water flow. There are the needed 'water closets', but also a range of rooms making up the complex of tepidarium, caladium and frigidarium. With a bit of careful observation, the mass of stones can be interpreted.
Chesters is know for one unexpected architectural feature in particular. You can see phalluses carved into the stone under the original floor line - there to be a good luck (apotropaic) charm and intended to be hidden by the floors, they're now visible to the naked eye.
As with other sites on the wall, the English Heritage website is really useful, and even includes a 'Step Inside' activity guide which might be useful when planning to take children. During the holidays they even run things such as a Children's Roman Solider day, so it's worth keeping an eye on the website when planning a visit.
There's plenty of parking at the front of the site, which is well-signposted from the main road (the B6318). There's a small gift shop with some amenities. The museum offers some shelter in case of bad weather, but the site is quite exposed. You will need to be careful down by the river.