Walkers and cyclists have been warned to be alert after large protruding spikes were “clearly maliciously placed” in a popular walking spot.
South Wales Community Mountain Rangers have issued a warning to all dog walkers, hikers, cyclists in the area to beware as there may be more.
Dean Hughes, South Wales Community Mountain Ranger safety officer, said: “The home made blocks of wood with large nails in them are very dangerous and they can be very hard to see.
South Wales Police have said that mountain users should be “extra vigilant”.
In February this year a 4x4 user got a flat tyre after driving over one of the deadly-looking spikes on Bwlch Mountain.