Sentence:  As impossible as it seemed, all the prizes had come from the cracker, but Sally had no idea how. When the old woman had said the cracker was unusual, Sally hadn't thought she meant that it was bigger on the inside than it appeared on the outside! A veritable <WSD>Tardis</WSD> in fact. 
Meaning of the word marked with <WSD> tags:  Something which resembles such a machine, either in that it travels through time or in that its interior is or appears to be larger (or more full of information or things) than its exterior suggested.