1000 years later, all human being live underground because of the high temperature.

They rely on the energy collecting system on land. Someday the energy collecting machine are broken. People need to go upland to fix it.

I designed a suitcase for those people, it looks like a box but it can transform to different shapes, and each shape has different function. This suitcase made by high temperature resistant material. People can use it to carry food, tools, etc when they go upland.