The Lincolnshire loop line was a 58-mile (93 km) double-track railway built by the Great Northern Railway, that linked Peterborough to Lincoln via Spalding and Boston.
The Lincolnshire loop line was authorised on 26 June 1846 as part of the London and York Railway bill. The then renamed Great Northern Railway purchased the Witham Navigation and all navigation rights the same year and began construction of the new line, partly beside the river, in 1847. The line opened in 1848 and was for a short period the main route to the north and Scotland until the line from Peterborough to Retford was opened in August 1852. Closure came in sections: the first was Woodhall Junction to Boston which closed to passengers and goods on 17 June 1963.
The line from Lincoln to Boston was known as the Witham loop because it followed the course of the River Witham, passing through Washingborough, Five Mile House, Bardney, Southrey, Stixwould, Tattershall, Dogdyke, and Langrick. The line from Boston to Spalding passed through three intermediate stations, Kirton, Algarkirk and Sutterton, and Surfleet; much of this section is now under the A16 road. The final section to Peterborough also had three intermediate stations, Littleworth, St James Deeping, and Peakirk. This section is the only part of the line that remains in operation, although most of the stations have long been closed and disused.