Through the movie Voyage Home Kirk and crew are in a Klingon vessel. At the end Scotty has two grown humpback whales beamed into the ship. How did both fit in the vessel if it's not that big of a ship?
Humpback whale adults range in length from 12-16m (Wikipedia). That's a pretty large mammal, but not gigantic by starship standards. The bridge of the ship, where we usually saw the crew, was small, but the whales were in a cargo hold. The external view of the Klingon ship made it appear big enough to have a sufficently large hold, though without much spare room for the whales to do much swimming. Presumably Spock explained to the whales that they would be confined to tight quarters for a while.