Glasgow Subway system is celebrating its 115th anniversary.
Opened on 14 December 1896, it is the third oldest underground metro system in the world after London and Budapest.
The system was converted from a cable railway to electric power in 1935 and it was closed between 1977 and 1980 for a major revamp which saw stations rebuilt and enlarged.
Subway operator, Strathclyde Partnership for Transport (SPT), is marking the anniversary with giveaways.
One year's free Subway travel will be up for grabs, along with free ticket offers for 115 other Subway users.
Passengers on Wednesday will also have the chance to win one of 115 chart albums and an Ipod Touch.'National icon'
Scotland's only underground was originally built for the Glasgow District Subway Company and originally powered by a clutch-and-cable system.
There was one cable for each direction, driven from a steam-powered plant on Scotland Street between West Street and Shields Road stations.
Earlier this year, the Scottish Government approved SPT's plans to carry out a multi-million pound upgrade of all 15 stations, bring in new "driverless" trains and introduce electronic smartcard ticketing.
The subway runs on a loop almost 6.5 miles (10.5 km) long which extends both north and south of the River Clyde.
SPT chairman Jonathan Findlay said: "The Glasgow Subway is truly a national icon. It's marvellous to think that it has been serving the city for well over a century and long before the first and second world wars.
"It's worth remembering that it would take 400 extra double decker buses a day to carry the same number of people across the city that the Subway can."
"That is why SPT is pushing ahead with work to modernise the Subway and I'm sure it will still be 'shoogling' residents and visitors alike in another 115 years time."