Folding bicycle small enough to fit in hand luggage
My cousin designed and built a prototype of a folding <i>trike</i> that fit in a suitcase. He'd check it on a trip, and on arrival unfold it. Then mount its case on the back and <i>put his normal suitcase in that</i>. He could then tour around whereever independently with his luggage. Had a blast touring Costa Rica he said.