The Imagination Station is his TARDIS. Because a properly-working TARDIS has a chameleon circuit, this would explain why it has been known to take on different appearances through the history of the show (having been described as resembling "a helicopter cockpit", "a hot water bottle turned on its side", etc.) The Imagination Station is a time machine of sorts - even though Whit claims that it's only a simulation, it has been established that injuries sustained on Imagination Station adventures can carry over to real life, suggesting that it may be real, as it would be with traveling in a TARDIS.