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This bell-shaped hall, 11.35 meters high, is named "Cloche de Fontis". Halls
like this are frequently the way abandoned quarries erode: the ceiling of the
quarry collapses in, leaving the ground above with little support, which in
turn collapses into the quarry. This hall was formed this way, and reaches
almost to the surface, where its destructive and unannounced arrival could
cause a serious accident. This hall was reinforced using a layer of sprayed
liquid concrete to avoid further collapse of the sand, clay and limestone
(the brown and black layers seen here) of the ground above.
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Go back through the long tunnel.
Examine the map.
Walk through to the exit.
