This spider's web of narrow tunnels, complete with coffin-sized cavities, opens out into dark subterranean churches - a most evocative way to end an underground tour of Rome.

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In the guided tours category, those ideas include the Seattle Underground Tour, which takes visitors through parts of Seattle buildings that were largely built over after the Great Fire of 1889.

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Kitsch roars its dinosaury head at Grand Canyon Caverns, luring you 21 stories underground for an ubercool cavern tour and even an overnight stay.

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Nirvana had just finished a two-week tour of Europe, opening for the underground trailblazers Sonic Youth.

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To bypass the tour groups, visit the churches and underground cities early in the morning, at midday or near closing.

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