We plodded down the passage known as Broadway on a wooden boardwalk, listening to our footsteps on the slats. Over a railing, a jumbled pile of limestone shards gives an idea what the path used to look like; it follows parallel to the boardwalk like a quake-struck road.

There’s a surreal quality to walking in a vast space underground. Light and shadow switch roles, and everything that’s not directly lit settles beneath a hazy, comfortable gloom. At times, I’d catch myself looking at the wrinkled rock or graceful vaulted avenues — or even farther into the cave, at cascading slumps of butterscotch-colored dripstones — and feel as if I had somehow been transported into an antique postcard.

Walking through the cave today, it’s hard to imagine just how lively it used to be.

Bands would set up in the Rotunda and float music down the corridors to a dance floor at the end of Broadway. In summertime, ministers would bring their congregations out of the heat and hold services in a recess of the cave known as the Church. One of the more peculiar structures in the cave is a stone clinic, which Mr. Bransford thinks might have even been built by Nick and Mat. It was run by a physician named John Croghan, who bought the cave in 1839. Dr. Croghan suspected, as had been a rumor since Mammoth had been a saltpeter mine, that the cave’s pure air and climate were a natural cure for tuberculosis. He persuaded at least 13 patients to contract to live for a year inside the cave, in canvas huts placed at various heights.

“Sometimes, during tours, people were shocked half to death to see these ghostly figures emerge from those huts and ask about the outside world,” Mr. Bransford said.

It was Nick Bransford’s unfortunate job to blow a horn and summon the skeletal patients to their meals. After four months, the experiment was aborted when three of the patients reportedly died. Less than 10 years later Dr. Croghan died of tuberculosis.

Early tours were less structured than today’s, but in ways that made them more animated, too. Guides lit dazzling Bengal lights, giving travelers a flash of the cave wall’s fluted pockets or the majestic height of a dome. On Echo River, they would paddle parties out in small boats and entertain them with a song; a stanza later they would be duetting with the sound of their own voice. Occasionally, inspired by the demonstration, a visitor would draw his pistol and fire, sending a barrage of explosive echoes thundering back.

One time, while Bishop was taking a party over the river his boat tipped and all the lamps were extinguished. Through chin-deep water and in complete darkness, he led the tourists with the sound of his voice, until five hours later Mat Bransford arrived to save them.