The furnace drew air from an underground tunnel to beneath the grate where the fuel was placed.

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Mining firm Freeport said at least four miners were rescued at its Grasberg mine after an underground tunnel collapsed early on Tuesday.

BBC: Freeport's Grasberg copper mine

An underground tunnel will link the East and West campuses.

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Then, inspired by NYC's High Line, Fletcher Priest won the Green Infrastructure Ideas Competition with his proposal for an underground mushroom tunnel beneath the streets of London.

ENGADGET: Inhabitat's Week in Green: Bicymple, computer-age fossils and an underground mushroom tunnel

An effort to send rescuers through the collapsed mine tunnel to attempt an underground rescue was suspended last week, after a new cave-in killed three rescuers and injured six others.

CNN: Crews prepare for final rescue effort at Utah mine