In a city like Edinburgh there's always something new to discover, and many residents don't even know about the huge tunnel running under the city.
The Innocent Railway tunnel sits beneath Holyrood Park, and is entered in a quiet residential close behind St Leonard's police station. Once you're in, the end of the tunnel seems a fair distance away - and is in fact an impressive 517 metres long, reports the Scottish Daily Express.
Built in the 1820s, the tunnel was used to transport coal between Dalkeith and Edinburgh with horse-drawn carriages. This is where the name Innocent Railway comes from, as steam engines were seen as dangerous.
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However, stationary steam engines were used to haul the carriages through the tunnel itself. To everyone's surprise (not least the pit owners) the Edinburgh and Dalkeith Railway soon became more popular as a passenger service and carried 150,000 passengers in 1832, its first full year of operation.
Steam trains replaced horses in 1845 after the nine-mile line was taken over by the North British Railway company and it remained in operation until as recently as 1968. The tunnel under Holyrood Park was the first railway tunnel in Scotland, running deep beneath the rocky crags of Arthur's Seat into the heart of the city.
After falling into disrepair, the tunnel and the the section between St Leonard's and Craigmillar were restored and re-opened in 1981 as a pedestrian bike path. It has been part of National Cycle Route 1 since 1994. This is the 1264-mile route on the National Cycle Network, running in sections from Dover in Kent to Tain in Easter Ross.
The tunnel's long incline of 1:30 is a strenuous one when cycling uphill into Edinburgh (sadly there are no steam engines to drag you up the hill) but if you're heading east it is a long, smooth, easy downhill ride all the way.
These days, both walls along the entire length of the tunnel are covered in graffiti (some of it very good, some of it not so much) although it is very well-lit and is a popular, well-used path during daylight hours.
However, there have been sporadic reports of crimes such as robberies being committed on the path. And would-be muggers are not the only danger, as the path had to be closed in 2021 due to the danger of rockfall from the cliffs of Arthur's Seat.
