One mile of boardwalks loop through Porcelain Basin, the park’s hottest exposed basin. (The name comes from the area’s milky deposits of sinter, also known as geyserite.) The bleached basin boils and bubbles like some giant laboratory experiment and the ash-white ground actually pulsates in places. Check out the overviews from Porcelain Terrace Overlook, near the Norris Museum – views that, in the words of Rudyard Kipling, made it look ‘as though the tide of desolation had gone out.’
As you descend from the museum, veer left before the continually blowing fumarole of Black Growler Steam Vent, said to be the park's hottest. As with most fumaroles, this vent is higher than the basin floor and is thus without a reliable supply of water. Below here is the large but currently inactive Ledge Geyser.
Going clockwise, the boardwalk heads left past Crackling Lake, which bubbles like a deep-fat fryer, and the Whale’s Mouth, a gaping, blue hot spring.
The swirling waters of Whirligig Geyser and nearby Pinwheel Geyser became dramatically acidic in 2000, helping to support the green cyanidium algae and yellow cyanobacteria that create many of the stunning colors in its drainage channels. The color of these bacterial mats indicates the relative temperatures of the water, from very hot blues and whites (up to 199°F, or 92°C) to cooler yellows and greens (144°F, or 62°C) and even cooler beiges and dark browns (130°F to 80°F, or 54°C to 26°C). Nearby Constant Geyser used to erupt every 20 minutes or so but has erupted much less frequently in recent years.
A side path leads past Hurricane Vent to Congress Pool, which appeared in 1891 – the year scientists convened in Yellowstone for a geologic congress. The corner of Porcelain Basin at the end of the boardwalk is the fastest-changing and most active part of the basin and offers fine views toward Mt Holmes (10,336ft).
A footpath to Norris Campground leads off from here beside Nuphar Lake.