The Field Museum and Shedd Aquarium were so popular on their free-admission days Monday on Martin Luther King Jr. Day that tickets officially "sold out" for the day.
"Field Museum tickets are SOLD OUT for the day," the Field Museum tweeted just before 2 p.m. and posted to its website. "We apologize for the inconvenience and hope to welcome you on another day."
"Shedd Aquarium tickets are SOLD OUT this day. Please visit another day," the Shedd wrote on its website.
Monday, Jan. 16, was one of the pre-planned free-admission days at the Field Museum and Shedd Aquarium that lets Illinois residents spend a day at the museums for free.
At the Field Museum, tickets for free days can't be reserved in advance and can only be acquired at the museum, according to the museum's website. At the Shedd, "tickets must be reserved online before your visit."
"Free Admission Days are the perfect opportunity for Illinois residents to explore our general admission exhibitions with your family or a group of science-loving friends," the Field Museum wrote online. "Or, use these days to check out special ticketed exhibitions or a 3D movie with a discounted Discovery or All-Access Pass."
Good news for anyone who missed out on Monday's free-admission day: There are more free days already on the books.
Tuesday, Jan. 17, and Wednesday, Jan. 18, are designated Field Museum free days, as well as Jan. 24, Jan. 25, Jan. 31 and Feb. 1.
At the Shedd, upcoming free days include: Feb. 7, 8, 9, 14, 15, 16, 21, 22, 23 and 28.
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If there's any lesson to be learned today, it's to arrive to the Field Museum early to scoop up a free ticket while you can -- especially on days when many children are out of school.