A historic hole in the wall [ANSWER]

GM/SV please, it's a blue dot

for the record: my dad went there during the event and i visited all places 53 years later, 1-2 months before another event!

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1936

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It's the swimming pool of the Olympic Village of the games of 1936. It's in Elstal, 18 km to the west of the olympia stadium of Berlin.

Well done, all