They are helping to open the door and shed light on a unique piece of Scottish maritime lore.
And now, the keys to Scottish lighthouse history will be going under the hammer in the new year.
A collection of keys to the coastal buildings from across the UK will be going to auction in May as part of a special marine and nautical artefacts sale in Edinburgh.
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The 300-strong assortment is currently owned by Dan Marshall, a Scottish hotelier who ended up with two canvas bags of keys after striking a deal with a visitor to the Aultguish Inn on the road to Ullapool in 1999.
This mystery visitor is thought to have collated the original keys during the time when lighthouses were being adapted to becoming automated.
Initially, his plan was to decorate the walls of his hotel with the ornate objects until he realised each was labelled and tagged.
It soon became clear the unique artefacts were actually keys to the beacons of the sea, including those to 83 Scottish lighthouses and outbuildings.
Mr Marshall has subsequently made it his mission to write a book named Keys to the Lights about the stories of the collection which is due to be released in early January.
The 78-year-old brought the pieces to the Museum of Scottish Lighthouses in Fraserburgh in September to show them to curators and seek their opinions.
Despite the visit and interest from the museum, Mr Marshall is delighted to be entering the collection in a special sale.
He said: “I have been down to Edinburgh and had a meeting with Bonhams Auctioneers. They were impressed with the collection and will put them into a special Marine and Nautical Artefacts sale which they only hold once a year.
“The collection will be in the auction on May 7.
“It all is becoming very exciting as the new blockbuster film The Vanishing featuring Gerard Butler comes out in America in January and the UK in March but I have the actual keys for the lighthouse where the three keepers vanished – Flannan Lighthouse.
“I don’t think the curator will be pleased at me for taking them to auction, but Bonhams are excited, because it’s such a unique set.”
Mr Marshall is taking the keys to the city in February to have them photographed and be entered into the sale catalogue.
The auction will be held in Bonhams in Edinburgh on May 7.