Grand Prismatic Spring Complete Guide: Boardwalk vs the 'Fairy Falls Overlook' Trail

Located 13 kilometres (10 minutes' drive north of Old Faithful) along the Firehole River, Grand Prismatic Spring is the largest hot spring in the United States and the third-largest on Earth, measuring 112 metres (370 feet) across and 37 metres (121 feet) deep. Here is the top secret to know before arriving: if you only park at the main Midway Geyser Basin boardwalk lot, you cannot see the famous rainbow rings from eye level because of the steam and flat angle. To see the true postcard view, visit two separate car parks 1.6 kilometres apart.

1. View #1 (From Above, The Postcard Shot): The 'Grand Prismatic Overlook Trail' (2.4 km Round-Trip, 45 Mins)

Since drones are strictly illegal across all US National Parks, the National Park Service built an official elevated hillside viewing platform on the Fairy Falls Trail in 2017.

• Where to Park (Skip Midway Geyser Basin for the Overlook): drive 1.6 kilometres (1 mile) south of Midway Geyser Basin toward Old Faithful and turn into the Fairy Falls Car Park just south of the Firehole River bridge.
• The Easy 20-Minute Walk: walk 1.2 kilometres along the wide, flat gravel path beside the river, then climb a gentle 32-metre switchback ramp up the pine-covered hillside onto the Grand Prismatic Overlook Platform, looking straight down onto the deep sapphire-blue 87°C centre encircled by rings of emerald green, canary yellow and fiery tangerine-orange.
• Why Is It Rainbow-Coloured? The pure blue centre is too hot (87°C) for life, so it scatters blue light; as water cools outward across the shallow shelves, heat-loving microbes (thermophiles) containing chlorophyll and carotenoid pigments form living yellow, orange and rust-brown mats.

2. View #2 (Up Close in the Steam): The Midway Geyser Basin Boardwalk (1.3 km Loop, 30 Mins)

After visiting the Overlook, drive two minutes north to the Midway Geyser Basin Car Park, ideally on a warm, sunny afternoon when cool morning steam has cleared. Cross the Firehole River bridge to walk past the boiling cauldron of Excelsior Geyser Crater (which discharges 15,000 litres of boiling water per minute) and right alongside Grand Prismatic Spring, Opal Pool and Turquoise Pool.