Berry Pomeroy Castle, Devon

English Heritage.
The castle dates from the 15th century, and within the outer walls is a great 17th century Tudor mansion, now much ruined. The site is tucked away in a wooded valley, overlooking a steep drop. There is quite a lot to look at in the way of romantically ruined structures, and parts of the castle are quite well preserved. There is an audio tour. It’s worth a visit if you are in South Devon.
Berry Pomeroy Castle is one location where the satnav is less than helpful. If you enter the postcode into Google Maps, satellite view, you can see just why I found myself on the wrong road, going in the wrong direction, and a mile from the castle. I had to ask a local for directions. The roads in the vicinity are single track, with no visibility.

Richmond Castle, Yorks.

English Heritage
Richmond Castle stands on a rocky promontory above the River Swale, and overlooking the picturesque old town of Richmond. The castle is Norman, and the towering keep is unusually complete. Visitors can climb up inside it for panoramic views over the castle’s great courtyard, the wide cobbled market place of Richmond, and the land beyond. There is an exhibition space, and a garden, its origins contemporary with the castle, on a terrace overlooking the River Swale. Inside the circuit of walls is a broad spread of green, with the vertical lines of the well-preserved keep soaring above.
The castle is well worth a visit if you are touring in the area. The castle is in the town and there is no dedicated parking. It was here that I encountered the parking-disk system used in North Yorkshire, that involves obtaining a free cardboard disk from a shop (etc), setting your time of arrival, and leaving it on view in your car.
The old town itself is also interesting, as I recall.

Pickering Castle, Yorks.

English Heritage
An interesting castle built on top of a mound surrouded by a deep ditch, obviously a replacement for a Norman wooden + earthwork fortification. Much remains of the outer circuit of walls surrounding the ditch, but not so much of the stone keep. There are views from the top of the mound.
Worth a visit if you are touring in the area.

Helmsley Castle, Yorks.

English Heritage.
The castle, originally a medaeval fortress, later acquired a luxurious Tudor house within its walls. The castle was rendered unusable at the end of the Civil War. Later still, it was regarded as a Victorian romantic ruin.
Today, the circuit of walls is largely intact. Inside is a wide area of grassy lawn. The visitor enters via a gatehouse and can look at the half of the keep still standing, the other half having been blown up and allowed to fall into the moat. The Tudor residence is now used as an exhibition space. An audio guide is available.
The castle is definitely worth a visit if you are in the area. Other EH properties are nearby.

Cliffords Tower, York

The tower comprises an unusual quatrefoil shell wall, built on top of a high mound. It’s almost all that remains of York Castle. Visitors can climb to the top of the wall, which affords great views over the central parts of York. The middle of the tower, which may once have been roofed, is now an open courtyard. If I remember correctly, there are a few relics and exhibits to look at inside the tower.
If you’re disabled, check photos of the mound and tower before planning your visit 🙁
There is a pay car park nearby, but you probably don’t want to be driving around the centre of York during the day, and you may find access on foot or by bus less troublesome.

Crownhill Fort, Plymouth

This is a Victorian Fort built to defend Plymouth from attack. Obsolete for its original purpose, it was later used as a barracks. There is quite a lot to see, with gun emplacements, embankments, tunnels etc. The Fort is owned by the Landmark Trust. Unfortunately it is not open daily to the public, but there are pre-booked tours and events during the year. If you are interested, you should look on the website and book a tour or event. I found it a most interesting place to explore.
My sister just reminded me about this access nightmare – approaching from the north a right turn is required, and it took some time to escape a tangle of looping service roads and get on the other side of the dual carriageway.
(Looking at the digital mapping today, it appears that turning off onto the B3413 Crownhill Road may not work, and you have to continue south to the big A386/A38 roundabout and execute a U-turn. Another possibility is to take an early right turn at the Looseleigh Lane roundabout and then approach circuitously along the B3373.)

Tintagel Castle, Cornwall

English Heritage
The site is encrusted in Arthurian myth. In reality, dramatically sited low walls are all that remain of a 13th century castle. Some parts of the site have succumbed to sea erosion. The remains extend on both sides of a gorge that separates the headland from the mainland. Castle aside, it’s interesting to wander around the headland, which is littered with ancient remains. There are sea views.

View from Tintagel Castle
View from Tintagel Castle

Pendennis Castle, Cornwall

English Heritage.
The castle was built as one of Henry VIII’s coastal gun forts, and the site continued in use as a military strongpoint up to the Second World War. Besides the original castle, the site includes substantial stone-built barracks buildings from more recent times. Suggested visit time: about 2 hours. There is plenty to look at, with sea views, and you could also take a boat trip across the estuary to visit St Mawes castle nearby.

St Mawes Castle, Cornwall

English Heritage.
One of the best-preserved of Henry VIII’s coastal artillery fortresses. It is built in an interesting clover-leaf shape, and has been little altered. Be careful of headroom when exploring the upper parts – I banged my head so hard it felt like my neck had become shorter 🙂 It can be visited in conjunction with the larger Pendennis castle nearby, if you make a harbour ferry trip between the two.