As important as bosses are, where they are is just as important. The room or area they are in can mean all sorts of things, but mainly the room / area is either useful for the boss, or for you, or it is just plain atmospheric. For example, when you fight Ghirahim in Legend of Zelda: Skyward Sword, you just fight in a sacred room and thats all there is too it. On the other hand, in the Skeldritch (Also known as Capbone) battle from Legend of Zelda: Spirit Tracks, you have to actually utilise the things in the room to destroy it, namely the catapults.
Personally, I think that my favourite boss battle location is the void in Kingdom Hearts 2 where you fight the third Xemnas battle (The one where the dragon has the giant shield that you have to throw skyscrapers at). It is just plain epic.
Also note that if you do not know the name of the location, as boss battles (especially final boss battles) sometimes do not have a name as such, feel free to describe the area instead.
Can’t wait to hear what you have to say!