If its the Hafodfeddgar in powys. Just off the side of the hafren forest then yes there is some great things to see, from exposed tram rails, great samples of copper and lead. There is also i hand pump still in pretty go shape above a shaft.
To find the portal follow the famers road towards the farm till you hit the edge of there woodland, find the stream and follow it up to a waterfall. The portal will be on your right.
If you do visit please stay safe.
Scott Tanner
REDJACKET MINE EXPLORERS