colossal
The Great Buddha Hall 大仏殿 of Tōdai-ji 東大寺.
As is typical of such buildings, the hall is situated at the end of a huge yard enclosed by a tall wall, the front gate of which (the Middle Gate 中門) is normally kept closed. As such, when you approach on foot via the Great South Gate 南大門 and along the stone path – surrounded by deer – you don't get any hint of what the building really looks like or just how large it is. While you can see the peak of roof, the distance makes it hard to imagine its overall dimensions. It's only once you go left, up through the entry at the far end of the wall and inside, that you get your first full view of the structure.
And it is tremendous, and this photo is not very useful for understanding its scale.