The volunteer-run tourist attraction has had train carriages damaged and bins have been tipped onto the track.
The incidents have all been reported to the police, but the most recent occurrence has caused more concern.
Marketing and events manager Nic Cullens explained: “In addition to the vandalism on Sunday evening, a large rock was placed on the line, which had it not been spotted, would have derailed the train.
“The train doesn’t go that quickly, but it could have been very difficult for the people on the train.
“We’ve had a couple of incidents that we’ve reported to the police, but we’ve been fairly stoic about it, because we thought it was just kids messing around.
“But this time, it’s a bit more serious with the rock, so we’re going to hand over the CCTV footage.”
The railway is primarily led by volunteers, who have had to work hard to repair the damage caused by the vandals on each occasion.
Nic added: “The people we feel most sorry for are the volunteers. They give their time and money to make the place look good and to see it destroyed is so disheartening.”
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