Excelsior Geyser and the Grand Prismatic Spring.
Excelsior is a dormant geyser, still emitting clouds of warm vapor that roll over the boardwalk and often block the view of the blue pool below.
The Grand Prismatic Spring is a hot spring, the largest in the US. You can't swim in it, but you can walk along the boardwalk. The actual spring is in 📷6 - the blue center is surrounded by a red microbial mat. Water slowly seeps out of the spring to all sides, including below the boardwalk, as seen in the other photos.
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