The Mill Folly Grotto including stone bridge, south of the Afon Llifon is a Grade II listed building in the Gwynedd local planning authority area, Wales. First listed on 8 September 1998. Garden feature.

The Mill Folly Grotto including stone bridge, south of the Afon Llifon

WRENN ID
half-step-bracken
Grade
II
Local Planning Authority
Gwynedd
Constituency
Dwyfor Meirionnydd MP: Liz Saville Roberts (PC)
Country
Wales
Date first listed
8 September 1998
Type
Garden feature
Address
The Mill Folly Grotto including stone bridge, south of the Afon Llifon, Glynllifon, Llandwrog
OS grid reference
SH 458 553
Coordinates
53.0728, -4.3018
Source
Cadw listing

Also on this page: flood risk · radon risk · weather exposure · detailed attributes ↓

Description

The Mill Folly Grotto, located south of the Afon Llifon, is a Grade II listed irregular rustic rubble garden feature dating from the 19th century. It features picturesque pointed arches and is arranged over two levels. The lower level contains a pool, while a bridge carries the footpath over the outlet into the Afon Llifon. The structure includes a complex series of grotto-like spaces, with an underground chamber accessed by a narrow passage and an additional small chamber at the lower level. The pool is supplied by a reservoir located on the hill towards Fort Williamsburg, connected by a leat from the top of the cascade to the east. The single-arch rubble bridge has voussoirs and a modern timber deck.

Local climate

The Mill Folly Grotto including stone bridge, south of the Afon Llifon sits in one of the wettest parts of the UK, with an average of 1,370 mm of rain a year. This makes it wetter than 97% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 98% of listed buildings.

It experiences an average of 20 freeze-thaw cycles a year, fewer than 78% of listed buildings. Of these, 9 follow at least 1 mm of rain in the preceding 48 hours. Average temperatures at this location have risen by 0.3°C per decade since 1991.

Averages for 1991–2020; temperature trend 1991–2025. Figures describe the wider area (a grid cell of roughly 10 km), not the individual site. Contains modified Copernicus Climate Change Service information 2026.

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Nearby listed buildings

  1. Western Cavern north of the path near main east vista fountain Grade II 70 m
  2. Footbridge over Afon Llifon to east of house Grade II 78 m
  3. Cascade at Glynllifon Grade II 83 m
  4. Fountain at end of east vista Grade II 88 m
  5. Eastern Cavern north of the path near main east vista fountain Grade II 97 m
  6. Ionic Column on former East Drive Grade II 109 m
  7. Bridge over Afon Llifon to south-east of Glynllifon House Grade II 175 m
  8. Dovecote and attached range to left at south-east corner of farmyards at Glynllifon College Farm Grade II 189 m
  9. Fountain pool including iron pipe in Coed y Terrace wood south-west of the Farm Grade II 196 m
  10. Former Cowhouse to south-west side of upper farmyard at Glynllifon College Farm Grade II 198 m