Dunster Castle was positioned on a steep, 200-foot (61 m) high hill.
Geologically, the hill is an outcrop of Hangman Grits, a type of red sandstone.
During the early medieval period the sea reached the base of the hill, close to the mouth of the River Avill, offering a natural defence and making the village an inland port.

Nearby is the Dunster Park and Heathlands Site of Special Scientific Interest noted for nationally important lowland dry heath, dry lowland acid grassland, wood-pasture with veteran trees and ancient semi-natural oak woodland habitats.
The fauna of the lowland heath includes the heath fritillary (Mellicta athalia), a nationally rare butterfly.
The assemblage of beetles associated with the veteran trees is of national significance because of the variety and abundance of species.

Along with the rest of South West England, Dunster has a temperate climate which is generally wetter and milder than the rest of England.
The mean annual temperature in the area is 8.3 °C (46.9 °F) with a seasonal and diurnal variation, but due to the modifying effect of the sea the range is less than in most other parts of the UK.
January is the coldest month, with mean minimum temperatures between 1 and 2 °C (34 and 36 °F).
July and August are the warmest months in the region, with mean daily maxima around 21 °C (70 °F).
In general, December is the month with the least sunshine and June the month with the most sun.
The south west of England has a favoured location with regard to the Azores High when it extends its influence north-eastwards towards the UK, particularly in summer.
Cloud often forms inland, especially near hills, and reduce the amount of sunshine that reaches the park.
The average annual sunshine is about 1,600 hours.
Rainfall tends to be associated with Atlantic depressions or with convection.
In summer, convection, caused by the sun heating the land surface more than the sea, sometimes forms rain clouds and at that time of year a large proportion of the rainfall comes from showers and thunderstorms.
Annual precipitation is around 800 mm (31 in).
Local weather data is collected at Nettlecombe.
Dunster Castle was positioned on a steep, 200-foot (61 m) high hill. Geologically, the hill is an outcrop of Hangman Grits, a type of red sandstone. During the early medieval period the sea reached the base of the hill, close to the mouth of the River Avill, offering a natural defence and making the village an inland port.
Nearby is the Dunster Park and Heathlands Site of Special Scientific Interest noted for nationally important lowland dry heath, dry lowland acid grassland, wood-pasture with veteran trees and ancient semi-natural oak woodland habitats. The fauna of the lowland heath includes the heath fritillary (Mellicta athalia), a nationally rare butterfly. The assemblage of beetles associated with the veteran trees is of national significance because of the variety and abundance of species.
Along with the rest of South West England, Dunster has a temperate climate which is generally wetter and milder than the rest of England. The mean annual temperature in the area is 8.3 °C (46.9 °F) with a seasonal and diurnal variation, but due to the modifying effect of the sea the range is less than in most other parts of the UK. January is the coldest month, with mean minimum temperatures between 1 and 2 °C (34 and 36 °F). July and August are the warmest months in the region, with mean daily maxima around 21 °C (70 °F). In general, December is the month with the least sunshine and June the month with the most sun. The south west of England has a favoured location with regard to the Azores High when it extends its influence north-eastwards towards the UK, particularly in summer. Cloud often forms inland, especially near hills, and reduce the amount of sunshine that reaches the park. The average annual sunshine is about 1,600 hours. Rainfall tends to be associated with Atlantic depressions or with convection. In summer, convection, caused by the sun heating the land surface more than the sea, sometimes forms rain clouds and at that time of year a large proportion of the rainfall comes from showers and thunderstorms. Annual precipitation is around 800 mm (31 in). Local weather data is collected at Nettlecombe.
Dunster