Cors y Llyn National Nature Reserve, near Builth Wells

What's here


The peaceful reserve of Cors y Llyn has one of the best wildflower meadows in Mid Wales and some of the trees here are only a few feet tall even though they are over 100 years old.

The meadow comes to life in spring and summer when a wealth of wildflowers, including orchids and Dyer’s greenweed, attract colourful butterflies.

The short accessible walking trail goes alongside the wildflower meadow and along a boardwalk past the stunted forest.

You can also explore the fields within the reserve, but please keep to paths if there is a hay crop growing. There may be grazing livestock.

Walking trail

The walking trail is waymarked from start to finish.

Look out for the information panel at the start of the trail.

Find out about walking trail grades.

Cors y Llyn Walk

  • Grade: Accessible
  • Distance: ¾ mile/1.3 kilometres
  • Trail information: Please keep to the boardwalk and paths – there are areas of deep open water and deep steep-sided pools covered with floating vegetation. Waterproof shoes or boots are recommended for visits between autumn and early spring as water can seep up through the boardwalk. Livestock graze parts of the reserve – do not approach or try to feed them. Keep dogs under close control and please shut gates behind you.

Just beyond the gate from the car park, the path goes alongside the wildflower meadow and then skirts around a pond where there is a bench.

The boardwalk then winds through the swampy woodland and past the stunted forest, before a gentle incline back to the car park.

What to see at the National Nature Reserve

Cors y Llyn is a National Nature Reserve.

Cors y Llyn means “bog of the lake” and the bog and fenland was once a lake.

The two basins which form the core of the reserve were originally carved out by glaciers during the last Ice Age and filled with meltwater.

Over thousands of years, they gradually became choked with vegetation, stones and earth, to create the rich, mixed habitats at the reserve today.

The basins support a range of acid-loving plant-life, with abundant bog-mosses, ling, cranberry, cross-leaved heath and the insectivorous round-leaved sundew. At the edges, there are patches of bog asphodel.

The southern basin has its own distinctive character: the Scot’s pine here is severely stunted, Scandinavian style, because of the water-logged peat.

A ribbon of birch wood and fen surrounds the bog.

Over 100 flowering plant species have been recorded in the meadow, including heath-spotted orchid, carnation sedge, lesser skullcap and sneezewort.

The landscape and wildlife varies at Cors y Llyn National Nature Reserve depending on which time of year you visit – here’s what to look out for.


Look out for pale-pink patches of colour in the meadow – these are the cuckoo flower which is one of the first flowers to bloom in very early spring.

A host of spring flowers follow this early display, including the heath spotted orchid, marsh violet and meadow thistle.


The meadow is at its best in summer with its wealth of wildflowers attracting lots of butterflies on warm, still days.

There is a colourful display of damselflies and dragonflies near the pond in summer, too, including some larger ones like the emperor and the southern hawker.

If you’re in luck, you might have the rare privilege of spying a hobby, catching these insects on the wing.

Look out for pied flycatchers, redstarts and wood warblers – the Welsh oak woodland summer visiting trio.


The brightly coloured mosses and lichens will help to brighten up even the dullest of days.

Listen out for the croak of the common frog as you walk past the damper areas.

You may also catch sight of a common toad and palmate newt.


Birds that visit the reserve during winter include woodcock and snipe.

National Nature Reserves in Wales

There are over 70 National Nature Reserves in Wales.

National Nature Reserves are places with some of the very finest examples of wildlife habitats and geological features.

Find out more about National Nature Reserves.

Accessibility information

There is a 250 metre path from the car park to the start of the boardwalk.

This path is mainly level and covered with mesh in places but has some uneven sections. The surface can be muddy after wet weather.

There are two gates before the path reaches the boardwalk.

The boardwalk is accessible.

There are benches along the boardwalk and passing places for wheelchair users.

Closures and diversions

Sometimes we need to close or divert trails for your safety whilst we undertake maintenance work or other operations.

We may have to close a site in extreme weather, such as high winds or snow and ice, due to the risk of injury to visitors or staff.

Please always follow any instructions on site and any temporary diversion signs.

How to get here


Cors y Llyn is 3½ miles north west of Builth Wells.

It is in the county of Powys.

Ordnance Survey map

Cors y Llyn is on Ordnance Survey (OS) Explorer map 200.

The OS grid reference is SO 016 556.


Take the A470 from Builth Wells towards Rhayader.

After 3¼ miles, turn left onto the minor road, signposted Cwm-bach Llechrhyd.

Take the second left and follow this narrow lane alongside a privately-owned yard with farm buildings on the right.

The road continues past the yard and on to the small car park at the entrance to Cors y Llyn.

Public transport

For details of public transport visit the Traveline Cymru website.


Parking is free of charge.

Overnight parking is not permitted.

Contact details

There are no staff at this location.

Contact our customer team for general enquiries during office hours, Monday to Friday.

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