Cadw’s annual Open Doors festival has returned, giving people across Wales the chance to explore more than 200 historic sites - including several in Brecon and Radnorshire - free of charge.

Close to home, the Brecon Royal Observer Corps Monitoring Post offers a rare insight into the Cold War. Visitors can descend 15 feet underground to see the restored post and original communications equipment, with ex-ROC personnel explaining their work monitoring nuclear threats. The post is open on Saturday, September 13 from 11am-4pm, with prior booking recommended.

Meanwhile, Abercamlais House and Gardens, five miles from Brecon, opens on Saturday, September 13 and Sunday, September 14 from 12pm to 4pm. The Grade I listed mansion, with origins in the Middle Ages and later 18th- and 19th-century additions, will host guided tours of the house and grounds, including its dovecote and parkland along the Camlais stream.

Other local sites taking part include:

• St David’s Church, Llywel – historic Grade I church with the Llywel stone, Saturday, September 13, 11am-4pm, no booking required.

• St Ellyw, Llanelieu – 13th-century church in the Black Mountains, open Friday, September 5 – Tuesday, September 30, 10am-4pm.

• St Anno, Llananno – home to a 16th-century rood screen and loft, open for self-guided visits Friday, September 5 – Tuesday, September 30, 10am-4pm.

• Powys Archives, Llandrindod Wells – tours of historic records on Saturday, September 13, 10am-1pm, booking required.

• Radnorshire Museum, Llandrindod Wells – guided tours on Saturday, September 13, 1:30pm-3:30pm, booking recommended.

Visitors are advised to check the details of each event as ticket requirements vary.

Dr Ffion Reynolds, Cadw’s Senior Heritage Events and Arts Manager, said: “By welcoming visitors free of charge, we’re opening pathways to experience the depth of Welsh history and culture and encouraging each person to help preserve these remarkable locations for future generations.”

Visit cadw.gov.wales/visit/whats-on/open-doors for more information.