The great escape is on at Canterbury Museum with an Asian elephant and a blue whale proving to be a logistical challenge to move.
The 1867 site is undergoing a $205m development, which involves demolishing large parts and restoring other historic areas.
Director Anthony Wright said packing away all the precious pieces will take until April 2023, as each item has to be carefully wrapped and then catalogued.
He said one of the museum's first acquisitions was an Asian elephant, which is currently trapped in the attic.
Wright said it was locked in with concrete after work was done following the Canterbury earthquakes.
"Part of that floor is coming out again to make a lecture theatre so there will be some way of getting it out.
"But now you've reminded me that that is probably one of the hardest ones to get out," Wright said.
The bones of a 26 metre-long blue whale are also providing difficult, given their weight.
Museum registrar Scott Reeves said they will have to open up the roof and crane the bones out of the building.
"Some of the smaller bones are going to be in the hundreds of kilograms let alone the massive skull and the jaw bones of it.
"It's the largest blue whale we've got evidence for in the world," Reeves said.
The museum will be closed for five years during the revamp, but will continue to operate using a pop-up venue in Christchurch.
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