Credit: Darrow Montgomery

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What exactly is the about 5-10 story concrete structure jutting out from the parking garage at the intersection of 3rd Street and Massachusetts Avenue NW, right after the I-395 tunnel?

Yeah, that’s a weird one, isn’t it? The answer, though, is about as boring as possible: It’s an air shaft. It was built in 1975 to ventilate exhaust fumes from I-395, which runs under it. It got muralized in 1988 to create a mirage of transparency with the Capitol dome behind it, although the actual Capitol is not remotely in that direction. And according to Mount Vernon Triangle Community Improvement District director Claire Schaefer Oleksiak, it’s not going anywhere, since it can’t be relocated as long as the freeway requires the exhaust fans it houses.