A stunnel was a portmanteau of Stellar Tunnel, an interstitial connection which could be used for interplanetary or interstellar transport.

The Interstitial Mass Transit System planned to create a stunnel to connect Mars with Arcturus. (PROSE: Transit)

When the Daleks attacked Pluto's moon, Charon, a group of human scientists researching the abandoned technology managed to create a stunnel to escape. (PROSE: GodEngine)

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