:Allt Cynhelyg

{{Use dmy dates|date=September 2019}}

{{Short description|Protected woodland in Powys, Wales}}

{{Infobox SSSI

|name= Allt Cynhelyg

|image=

|image_caption=

|aos= Powys

|interest= Biological

|gridref={{gbmappingsmall|SO0266747173}}

|coordinates = {{coord|52.114282|-3.4228349|display=inline,title}}

|displaymap= Wales

|area= 14.63 ha

|notifydate=1 January 1972

|enref=

}}

Allt Cynhelyg is a semi-natural oak-hazel woodland forming a Site of Special Scientific Interest in Brecknock, Powys, Wales.{{Cite web |title=#GetOutside: do more in the British Outdoors |url=https://getoutside.ordnancesurvey.co.uk/https://getoutside.ordnancesurvey.co.uk/ |access-date=2022-07-10 |website=OS GetOutside |language=en-gb}} It has a notable natural population of Meconopsis cambrica (Welsh poppy).