If you're now in an apocalyptic mood, you can also check out Budapest's subway shelters. The two socialist-era subway lines were designed to double as shelters

If you're now in an apocalyptic mood, you can also check out Budapest's subway shelters. The two socialist-era subway lines were designed to double as shelters in case of an emergency, and there's pretty substantial infrastructure built out to enable this usecase: gates to seal the tunnels, air and water supply systems, storage rooms, toilets. Occasionally there are drills [1] to practice for a real emergency. The linked article contains some fascinating pictures in their gallery, when you advance after clicking any of the embedded ones. Combine with the fact that some of the rolling stock is still Soviet vintage, for that extra Metro 2033 feel. As for other underground passages, Budapest has several caves too [2][3][4], and a set of passageways that connect the famous Gellert Baths with its historic source deep in the mountain [5] and now contain mechanical rooms and other boreholes for the Baths' thermal water that are further from the Danube, so they don't mix in times of high water. [1] http://iho.hu/hir/amikor-dizelmozdony-jar-a-metroalagutban-111118 http://iho.hu/hir/amikor-dizelmozdony-jar-a-metroalagutban-1... [2] http://www.dunaipoly.hu/hu/helyek/bemutatohelyek/pal-volgyi-barlang http://www.dunaipoly.hu/hu/helyek/bemutatohelyek/pal-volgyi-... [3] http://www.dunaipoly.hu/hu/helyek/bemutatohelyek/szemlo-hegyi-barlang http://www.dunaipoly.hu/hu/helyek/bemutatohelyek/szemlo-hegy... [4] https://en.wikipedia.org/wiki/Gell%C3%A9rt_Hill_Cave https://en.wikipedia.org/wiki/Gell%C3%A9rt_Hill_Cave [5] https://www.nlcafe.hu/foto/20150410/alagut-gellert-hegy-alatt/ https://www.nlcafe.hu/foto/20150410/alagut-gellert-hegy-alat...