Yarmouth Castle is a square fortification, nearly 100 feet (30 m) across, with an arrow-head bastion protecting the landward side.
The north and west walls face the sea, protected by angular buttresses, and a 10-metre (33 ft) wide moat originally protected the south and east side, although this has since been filled in.
The castle's 16th-century bulwark, which originally covered the area to the west of Pier Street and the north of Quay Street, and its quay battery have also been destroyed.

The walls of the castle are mainly built from ashlar stone, with some red brick used on the south side.
The walls are pierced by a small number of gunloops, including in the "ears" of the bastion, which would have overlooked the moat.
When first built the interior of the castle formed a sequence of buildings around a courtyard, but the southern half of the castle was filled in shortly afterwards to produce a solid gun platform able to support heavy guns.
It was later raised again in the 17th century to its current height.
The parapet is now covered with turf, with 19th-century rounded corners, and the platform still has the rails on which the four naval guns would have traversed, dating from 1855.
A small lodging room, built on the platform at the top of the stairs, has since been destroyed.

The arrow-head design of the castle's bastion reflected new ideas about defensive fortifications spreading out from Italy in the 16th century.
Earlier Henrician castles had used the older European style of semi-circular bastions to avoid presenting any weak spots in the stonework, but an arrow-headed design enabled defenders to provide much more effective supporting fire against an attacking force.
Yarmouth was among the first fortifications in Europe, and the first in England, to adopt this design.

The accommodation and other facilities are on the south side of the castle.
On the ground floor, the entrance to the castle leads through to a courtyard, linked to four barrel-vaulted rooms in the south-west corner, originally 17th-century lodgings for the garrison.
Two of these chambers were converted for use as magazines and the fittings of one of these still remains in place.
In the south-east corner is the Master Gunner's House, comprising a parlour, hall and kitchen on the ground floor, and a chamber and attic on the floors above.
The parlour and hall would have originally been separated by a screen; the chamber would also have been subdivided.
On the first floor is a small chamber, supported on arches above the courtyard, which was used as a lodging.
On the second floor, the Long Room runs on top of the barrel-vaulted chambers, its massive, original roof still intact.
Yarmouth Castle is a square fortification, nearly 100 feet (30 m) across, with an arrow-head bastion protecting the landward side. The north and west walls face the sea, protected by angular buttresses, and a 10-metre (33 ft) wide moat originally protected the south and east side, although this has since been filled in. The castle's 16th-century bulwark, which originally covered the area to the west of Pier Street and the north of Quay Street, and its quay battery have also been destroyed.
The walls of the castle are mainly built from ashlar stone, with some red brick used on the south side. The walls are pierced by a small number of gunloops, including in the "ears" of the bastion, which would have overlooked the moat. When first built the interior of the castle formed a sequence of buildings around a courtyard, but the southern half of the castle was filled in shortly afterwards to produce a solid gun platform able to support heavy guns. It was later raised again in the 17th century to its current height. The parapet is now covered with turf, with 19th-century rounded corners, and the platform still has the rails on which the four naval guns would have traversed, dating from 1855. A small lodging room, built on the platform at the top of the stairs, has since been destroyed.
The arrow-head design of the castle's bastion reflected new ideas about defensive fortifications spreading out from Italy in the 16th century. Earlier Henrician castles had used the older European style of semi-circular bastions to avoid presenting any weak spots in the stonework, but an arrow-headed design enabled defenders to provide much more effective supporting fire against an attacking force. Yarmouth was among the first fortifications in Europe, and the first in England, to adopt this design.
The accommodation and other facilities are on the south side of the castle. On the ground floor, the entrance to the castle leads through to a courtyard, linked to four barrel-vaulted rooms in the south-west corner, originally 17th-century lodgings for the garrison. Two of these chambers were converted for use as magazines and the fittings of one of these still remains in place. In the south-east corner is the Master Gunner's House, comprising a parlour, hall and kitchen on the ground floor, and a chamber and attic on the floors above. The parlour and hall would have originally been separated by a screen; the chamber would also have been subdivided. On the first floor is a small chamber, supported on arches above the courtyard, which was used as a lodging. On the second floor, the Long Room runs on top of the barrel-vaulted chambers, its massive, original roof still intact.
Yarmouth Castle