Contractors strengthening Edinburgh's Haymarket railway tunnels ahead of a regeneration project have released images of the underground works.
A team of up to 40 specialists is working through the night over 14 months.
The site above the tunnels will be home to The Haymarket, a £200m development of retail, offices and hotels, with an underground car park.
It is being developed by Edinburgh Haymarket Developments Ltd.
It is a joint venture between Interserve, the international support services and construction group, and Tiger Developments.
It is one of Edinburgh's biggest commercial projects of the last 10 years and is expected to create about 3,500 jobs.
David Westwater, Interserve development director, said: "This work is the main challenge before we can begin construction above ground.
"It will be early next year before we can do that, but then people will soon start to see the development taking shape.
"After such a long time as a gap site, we're very excited about what The Haymarket has to offer and how it will help to create a real gateway at Edinburgh's west end."
Angus MacGregor, BAM Ritchies' project manager, said: "We are very well experienced in complex rail projects but every situation is unique, so we've had to develop a very specific approach for this work based on the skills and knowledge of our team.
"There are many constraints to working on this site, but we have made good progress so far thanks to the working relationship we have with our client and Network Rail."
Gary Walker, from Network Rail Asset Protection, said: "Clearly our priority is to ensure that the works are carried out safely and with no disruption to rail passengers on this extremely busy section of the network.
"We have worked closely with Edinburgh Haymarket Developments and BAM throughout the design process over the last 12 months and it is pleasing to see work being carried out as planned."
The strengthening work will allow contractors to begin building the foundations for the development.
It includes grouting between the tunnel lining and the surrounding ground, and drilling and inserting metal bars within the brick lining.
Currently, engineers are only able to work in the north tunnel from midnight until 05:00 four nights a week and in the south tunnel from 01:00 to 09:30 one night a week.