A nesting box is just a box where a gravid turtle can lay eggs. This box is designed to stimulate a natural nesting site. In nature, turtles choose a place close to their natural habitat for nesting. This site usually has loose soil which is generally damp. When kept in an enclosure, gravid turtles will refuse to nest unless you create a nesting site for them. She may lay a few eggs in the aquarium, but usually, she would refuse to lay all the eggs. This situation is called egg binding and can lead to severe and serious complications. The eggs can break while inside her. This will lead to serious health issues. Alternatively, the egg can calcify inside her. If this happens, a surgical procedure will be needed to remove the eggs.