Linda Davidson/The Washington Post

If you let your imagination wander, it actually feels like a submarine on the ocean floor. Right there, after the metal detectors of the Commerce Department, a big blue hallway leads you down a few flights of stairs and the sound of a penny crank machine greets you before a long, black cavernous corridor. You might as well be underwater.

As a little boy, I first experienced the small wonders of D.C.’s National Aquarium. Electric eels and poisonous frogs? It was like nature had the coolest toys. Later, as a teenage camp counselor on field trips, I saw it in a new, more educational light. As a grown man, it still gave me a little spook when I entered.

Monday was the final day for the facility that’s been there since 1932. But it was business as usual, right up until the very end. The one-floor aquarium frequently got a bad reputation because of its basement location. Most people will tell you that they’ve been to the Baltimore facility and have never heard of the one on 14th Street NW. And it’s definitely not comparable to anything on a Smithsonian scale. But it has its own charm.

The music in the front sounds like something from James Cameron’s “Avatar.” The all-black paint scheme creates an illusion of size and mystery in a space that’s not actually that big. Yet, the bathrooms are still decidedly federal, with their rounded beige tiles on the wall, and smaller black and white square ones underneath your feet. Many of the people that walked through the doors Monday were there for the first time.

“It’s much more interesting and informative than I quite frankly thought it was. I’ve always heard it was in a basement and it just sounded like it was an afterthought,” Jerry Conlon, 64, said. He said he’s lived in D.C. for 42 years and found himself disappointed that this was his first trip. “I think I probably would have brought out of town guests here in the past, if I had known. They always called this Washington’s best kept secret, I think they’re right.”

The weekend was sort of a homecoming for old staff and volunteers. At the final shark feeding Monday, they gathered in their blue polo shirts to watch and took pictures together. It was an emotional experience for some. Lisa Pulaski, a volunteer diver at the Baltimore facility, was bummed that things had to come to an end. “To know that this is one of the oldest ones in the nation, it’s sad to see it finally closing down. It’s historical. You don’t want to see it go away, because it’s been here so long,” she said. “It’d be nice if they had another National Aquarium somewhere here on The Mall. … [But] I don’t know if that’s ever going to happen.”

The Hoover building is undergoing renovations, which is why these fish and other animals have to find new homes. What will become of this space is a sobering reminder of how banal federal life can be: plans are to use the space as a thoroughfare between the Reagan Building and the renovated space above. “A fancy word for a hallway,” one worker told a dismayed tourist Monday.

Around 4 p.m., the staff became visibly anxious. The final ticket sales are usually at 4:30, and the aquarium closes at 5, as it really only takes half an hour to see the whole thing. Workers gathered around the ticket desk, hugging each other occasionally and looking to share that final moment.

Yet, the last person to ever buy a ticket at D.C. National Aquarium was a man that made the decision to come just a few hours earlier. “Actually, I didn’t know it was closing until like 2 p.m. when my dad told me. I’d been meaning to come here for a while, so it was [a decision] just at the last moment,” Gabriel Olivero, 26, a Navy hospital corpsman who lives at Ft. Belvoir said. He was there with a female friend- it was the first visit for both of them.   “I thought maybe they’d just close it temporarily, but it turns out they don’t have any plans to come back. So, that kinda sucks,” he said.

After the final stub was sold, the last tour map was given and the gift shop — picked clean and nearly bare bones — rung up one more sale before shutting down, the inviting voice over on the house speakers felt louder than ever.

“The aquarium today is still a gem in our nation’s capital, providing an intimate experience,” she says as part of script that plays on repeat.

This day, yes. The next day, no.