This achievement was proposed in the past, but has been rejected, because of various opposing votes.. Please read the discussion page for more details.
As per the page proposed achievements: If an achievement has strong opposition and the reasons for opposition are not resolved through discussion, then the proposed achievements category is replaced with the rejected achievements category, the reason explained succinctly on the page, and the page otherwise marked to make sure it isn't confused with an achievements page.
In the game Portal the player uses the wormhole placing abilities of the Aperture Science Handheld Portal Device to find her way through various obstacle courses. Aperture Science has not given the ASHPD to any geohasher. Thats why geohashers need to stick to non-interdimensional tunnels.
Requirements
In this achievement, traversing tunnels (meaning everything tube-like that is longer than it's diameter) is encouraged. Try to cross as many subway stations, underpasses, children slides and so on. Every single tunnel (no matter of direction or how many times you transit) counts only once.
Proof
Take a photo of every tunnel you cross.
