The Wenallt

"The Wenallt is an area of ancient woodland located on the ridge overlooking Cardiff. It is surrounded by countryside yet is close to the built up area. A good path network reveals the wide variety of interests including ancient beech trees, bluebells and great wildlife."

http://www.cardiff.gov.uk/content.asp?id=545&d1=0

"Coed-y-Wenallt is an ancient woodland which means it
has been woodland since at least 1600AD. There are 44 hectares of native Oak, Hazel and Beech woodland. It is designated as a Site of Special Scientific Interest (SSSI) in recognition of its value for wildlife. Cardiff Council own and manage the site.

(PDF) http://www.cardiff.gov.uk/objview.asp?object_id=3632
"