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There’s a Russian holiday for veterans of the Frontier Guard. English Russia describes it thusly:

On the 28th of May Russian frontier guards traditionally celebrate their holiday. On this occasion soldiers and officers, former or not, jump into fountains, dance, sing military songs, generally speaking they enjoy themselves in a civilized manner…but not always.

Seems like the appropriate thing to do during any heatwave, unless of course there’s something even cooler than that, i.e., The Overnight Open Thread.