Survey work has begun at a disused Rhondda railway tunnel, with plans to reopen it to walkers and cyclists.
In January, the Rhondda Tunnel Society was
given a £10,000 grant from the Welsh Government to carry out an initial "tapping survey" on the tunnel, which runs from Blaencwm to Blaengwynfi in Neath Port Talbot.
Experts began work on the 3km-long (1.8 mile) tunnel at 08:00 BST on Wednesday.
The work is expected to last two weeks.
Steve Mackey, chairman of the Rhondda Tunnel Society, said it was an "exciting day".
He said specialist works and railway contractors Hammond ECS had started in Blaengwynfi by working to remove a concrete cap so they can begin an "exploratory drill" inside the tunnel.