The Beautiful singer turned down the chance to hire out the entire train for £25,000 and instead booked out a first-class carriage on the First Great Western service, according to British newspaper the Daily Mail.
Aguilera waited for the train at Paddington, which was specially decked out with white roses, candles, and champagne at her request.
The 30-year-old boarded the 2.15pm London Paddington to Cardiff Central service - and brought along boyfriend Matthew Rutler and an entourage of 22 people.
A source told the publication: 'Christina just sat back and enjoyed the views.
'She had been told the countryside is beautiful and she just wanted to see it. None of them fell asleep, even though they'd had a late night. They seemed to really enjoy the journey.
'Her management hired half the carriage through a company called Train Chartering because she didn't like the idea of a fleet of Bentleys sitting on the M4 for hours on end.'