Originally 'fantubular' (a mix of fantastic and tubular) it quickly evolved into the more pronounceable 'funtubular', which is used to describe an amazing or fantastic time or experience. Can be used to describe a person or place with fun or similarly tubular attributes.
"Oh, my GOD! Today was so funtubular! We went to the beach, the zoo, then back to the beach with the monkeys!"
"Dude, that Jim is totally funtubular. He just bought everyone passes for Disneyland."