Costigan's Needle

the long version

A field generator that encloses a portal to an unknown dimension is too small for anyone to look through, but when hands are extended through the opening, they disappear - along with as much of the arm of the tester as can fit. A much larger generator is constructed, a towering column with a door-shaped opening at the base resembling the eye of a needle. But before testing can occur, an imbalance in the power source explodes the field out of the eye. Most of the populace of a city block disappears into the portal. The journey back reminds one of Verne's "Mysterious Island" in that the castaways must use only the knowledge in their heads to invent their means of salvation.