Some people have been approached by the police recently when trying to cross the railway line to get to Blackwell Halt and/or Blatant Buttress in Chee Dale Upper.
The old approach used to go over the railway but it is a live railway live railway so this is illegal, hence the police being called (several times over the last year according to the latest report).
There is a tunnel though so there is no need to cross the live tracks to get to either crag (although Blatant is probably a bit close to the railway so there may still be objections to climbing here).
The description in the Rockfax is correct - From the Monsal Trail on the Chee Dale Upper Approach, head down towards the cafe/cycle hire. Cross the bridge and turn sharp left at the cottages and follow a small path along the edge of the river and past a pump house. This leads to a tunnel under the train tracks. On leaving the tunnel, cross the fence on the left and go up some hidden stone steps. From here a path leads up into the grassy field below the quarry.
Unfortunately the BMC Peak Limestone North book still has the old ‘cross the live railway line’ description – don’t foillow this.