After the fort, I would move the big boxes over to the sensory table. Again the idea was for children to crawl into the boxes and play in the sensory table from the space inside the boxes.
However, there have been several big box constructions that were not specifically made for children to go in. An example was the Big box on top. I set a large box over the top of the sensory table and embedded several cardboard tubes through it.
Below is one more example of an apparatus that beckoned children to experience it from the inside. I called it Big box big windows