The Three Peaks is a classic challenge which starts and finishes in the Blue Mountains in Katoomba, and tags Mt Cloudmaker, Mt Paralyser and Mt Guouogang. Bushwalking the Three Peaks in less than 48 hours has long been considered a badge of honour. John Fantini and Warwick Daniels set the FKT of 18h22min back in 1966. Their record stood for over 50 years, until trail runners Matthew Scholes and Loughlinn Kennedy shaved an hour off in 2018 (17h14min). Top Australian mountain runners and rogainers have acknowledged the savagery of the off-track section. Many attempts to finish the Three Peaks have been abandoned.
Start at the Water Board Ladders car park (known as the Climbers car park) on Glenraphael Drive. Your goal is to sign the logbooks at all three peaks then return to car park, taking any route your choose. Most people tackle Cloudmaker, Paralyser and then Guouogang, though even within this sequence there are options. For more details (accepted style, routes, history, trip reports, fastest times), see Ashley Burke's Three Peaks site.