Two hundred and twenty miles of cave, and nobody knows where it ends

Jewel Cave holds over 220 miles of mapped and surveyed passages, which
makes it one of the longest caves in the world. Its splendour shows in fragile
formations and glimpses of brilliant colour, and its maze of passages has been
luring explorers for decades.

The phrase the park service uses is worth quoting exactly: **its scientific
wealth remains a mystery**. Two hundred and twenty miles is what has been
mapped, not what exists. Surveying continues, and the cave keeps getting
longer — which makes this one of the few national monuments whose headline
number is provisional.

Getting there

By car. Jewel Cave is 13 miles west of Custer, South Dakota and **24
miles east of Newcastle, Wyoming**, on U.S. Highway 16. It is about **54 miles
from Rapid City** via U.S. Highway 16 / 385.

By plane. The nearest major airport is **Rapid City Regional, 63 miles
away**.

The weather above ground

Weather in the Black Hills varies a great deal through the year, and can be
drastically different between the northern and southern hills. These are
average lows to average highs at Custer, South Dakota:

Rain averages 19 inches a year, with May the wettest month. Snow
averages 48 inches.

Underground, none of that applies — a cave holds its own temperature, which is
part of why the surface forecast is the wrong thing to dress for.

*Location: National Monument, South Dakota. Source: U.S. National Park
Service.*