Though the Belle Isle Aquarium officially closed its doors to the public back in 2005, there's still one day a year when metro Detroiters can get their fill of early 20th century watery amusements. As part of Shiver on the River, Belle Isle's cold-weather celebration held annually in early February, the Belle Isle Aquarium opens for one day between 10 a.m. and 3 p.m. Visitors step through a Beaux Arts-style arched entryway into a veritable aquarium museum: When it closed, it was the oldest continuously operated aquarium on the continent. Though small by contemporary standards, the building pays homage to an earlier era in Detroit's history — and it still brings in the crowds. At this year's Shiver on the River, more than 2,500 people reportedly lined up for a look. Not so bad for an attraction that's officially closed for business.