Mammoth Hot Springs: The Travertine Terraces, 1891 Fort Yellowstone & the 1903 Roosevelt Arch

Located 8 kilometres (5 miles) inside the North Entrance at Gardiner, Montana, Mammoth Hot Springs is unique in Yellowstone: unlike Old Faithful and Norris, which sit over hard volcanic rhyolite rock that creates geysers, Mammoth sits over thick beds of ancient marine limestone. As hot, slightly acidic water rises through fault lines, it dissolves underground calcium carbonate and deposits up to two tonnes of chalk-white travertine rock on the surface every day, building a living hillside of cascading stone steps like a cave turned inside out.

1. Walking the 'Lower Terraces' Boardwalk & Driving the 'Upper Terrace Loop'

Because underground earthquakes shift the plumbing of the hot springs, some terraces dry to chalky grey while neighbouring terraces burst to life in white, yellow and tangerine-orange:

• The Lower Terraces Boardwalk (Start at 'Liberty Cap' or the Upper Lot): start at the bottom car park beside the 11-metre-tall stone cone of Liberty Cap and climb the wooden boardwalk stairs past Palette Spring, Minerva Terrace, Mound Terrace and turquoise-and-gold Canary Spring. To skip climbing 300 stairs uphill, drive to the Upper Terrace Car Park first and walk out onto the top of Canary Spring on a flat boardwalk.
• The One-Way 'Upper Terrace Drive' (2.4 km Scenic Car Loop): takes vehicles under 25 feet past Orange Spring Mound and skeletal trees engulfed in white mineral stone at Angel Terrace.

2. Historic 'Fort Yellowstone' & The 1903 'Roosevelt Arch' in Gardiner

• Fort Yellowstone & The Albright Visitor Center (Open 365 Days): across from the terraces stand 35 red-roofed sandstone buildings built by the US Army Cavalry in the 1890s. Dozens of wild elk lounge on the lawns between the hotel and Visitor Center (stay 25 yards back, especially during the autumn mating rut).
• The 1903 Roosevelt Arch (Gardiner, 10 Mins North): drive 5 miles north to Gardiner to photograph the monumental 15-metre basalt stone arch dedicated by President Theodore Roosevelt in 1903, inscribed with the founding law of the park: 'For the Benefit and Enjoyment of the People'.