Geoff Marshall and Neil Blake could tackle the Paris Metro next
The record for visiting all 275 London Underground stations has been broken by 43 minutes.
Geoff Marshall, 32, from Epsom, Surrey, and Neil Blake, 31, from Deptford, south-east London, recorded a time of 18 hours, 35 minutes and 43 seconds.
But they finished so late - 0005 BST - that they could not take a Tube home and had to hire a minicab.
It was seventh time lucky for Mr Marshall, whose earlier attempts were scuppered by train failures and injury.
Taking no chances this time, Mr Marshall spent about six days of practice runs before being joined by Mr Blake.
The pair are keeping their exact route a secret to protect the record, but they did begin at 0529 BST at Amersham in Buckinghamshire on the Metropolitan Line and ended at Upminster in Essex on the District Line.
Mr Marshall told BBC News Online that it became a personal challenge after completing the task for the first time for Cancer Research.
"We did not break the record that time, but it became something I became obsessed with," he said.
"I tried many times before, but not managed it because of the trains or injuring my knee."
Paris Metro challenge
It took four months for the Guinness Book of Records to acknowledge the feat.
"We had to send them digital photos with the time on from every station - we even got the driver of the last train we were on to confirm it," Mr Marshall said.
The challenge now could be the Paris Metro.
Mr Marshall said: "At the moment we are just joking about it over a few pints.
"But it's one of those things that could happen."