The castle is built on a woody escarpment dominating the small town.
Only a portion of curtain wall survives of the early keep mentioned in the Doomsday Book but a 13th century gatehouse remains almost intact.
The facade of the inner castle is largely Elizabethan, the main front being completed in 1589.
In 1617 a new house was built within the castle bailey incorporating part of the curtain wall.
At the time of the Commonwealth the old fortifications were demolished but the Jacobean house was left intact.
Dunster Castle has had a mainly peaceful history.
However, during the Civil War it first resisted the Royalists in 1642 and then was held as a garrison for them until 1645.
It finally fell to the Parliamentarians and orders were sent to have the castle demolished. However, these were not carried out and the castle remained a garrison for Parliamentarian troops for five years. On paying a fine the original owners were allowed to take up residence again and they set about renovating and improving the castle.
In the 19th century the architect Salvin was employed to embellish both the exterior and interior.
Salvin built the two great castellated towers and added the tower at the centre of the south side. He also modernised much of the interior but the carved oak staircase from the 1680s and the oak-panelled dining room with its splendid plaster ceiling, both commissioned by Colonel Francis Luttrell, were left untouched.
The castle is approached up a steep slope leading to a 15th century gatehouse.
Beyond it the second 13th century gatehouse is the oldest surviving structure of the castle. This gives access to the north facade where Salvin's Victorian additions blend well with the Jacobean wing. Only details in the New Red sandstone masonry show where one ends and the other begins.
A Victorian conservatory leads out on to a sheltered south-facing terrace. The garden stretches down in terraces to the banks of the River Avill. The mild maritime climate allows many semi-tropical plants to grow in the garden's sheltered spots.
The steep paths that curl around the hill are lined with rhododendrons, magnolias, fuchsias and hydrangeas. On the banks of the Avill is a restored 18th century mill that now grinds flour for sale. There has been a mill on this site since at least 1080.
Castle sometimes closed for private functions - see website.