PHOTO: Rendering of the In Memoriam exhibition at the 9/11 Memorial Museum

Tickets go on sale today for the 9/11 Memorial Museum, which will open to the public on May 21.

The first day is free to all visitors thanks to Conde Nast, who is sponsoring the historic opening day.

The media company is moving its headquarters to become the corporate anchor of One World Trade Center, overlooking the Memorial and Museum.

Advance reservations for museum tickets can now be booked at 911memorial.org. There are various admission discounts available, and admission will be free from 5 to 8 p.m. on Tuesday nights. Admission is free to 9/11 families and 9/11 rescue and recovery workers who are registered with the memorial.

The museum has two core exhibitions. “In Memoriam,” pays tribute to the people killed on 9/11 and in the 1993 World Trade Center bombing.

The other exhibition is more focused on the history of the event and tells the story of what happened on 9/11 at the three attack sites and around the world.

The museum is filled with monumental artifacts, photographs, audio and video footage and personal testimonials and memorabilia.

General admission to the museum is $24. Seniors, veterans and college students are $18. Admission is $15 for kids age 7 to 17.

The museum will be open for 9/11 families, volunteers and lower Manhattan residents and business owners impacted by the attack.