This geyser basin, 1 mile northwest of Old Faithful, has a few interesting features. The eponymous black sand is derived from weathered volcanic glass (obsidian). You can access Black Sand Basin by car or, better, by foot from Daisy Geyser. Rangers lead hour-long walks here daily at 1pm.
Cliff Geyser is named for the geyserite wall that separates the geyser from Iron Spring Creek and is a frequent splasher. Nearby Ragged Spring frequently joins in the action with 12ft bursts. Emerald Pool looks like an exquisite flower with a lovely orange lip and gets its pretty color from yellow bacteria that blend with blue reflected from the sky. Rainbow Pool is connected underground to nearby Sunset Lake and is one of the more colorful in the park, though it's hard to see. The ground under the boardwalks here is literally boiling.
Unsigned Handkerchief Pool, just to the south of Rainbow Pool, was once one of Yellowstone’s most famous features. Visitors would place a handkerchief in the pool and watch it get sucked down and then spat out ‘clean’ through a side vent. The pool stopped functioning in the 1920s after a dimwit jammed logs into the opening, but it has since restored itself. Today it’s illegal to throw anything into any of Yellowstone’s thermal features.