The Baphuon was built in the 11th century by Udayadityavarman II. Most of the temples in Angkor are either made of a series of concentric terraces, like Preah Khan, or else are in the shape of a mountain, like the Bayon. The Baphuon is an amazing, enormous example of the mountain style.
The Baphuon is reached by an enormous raised walkway. You go up a very sharply steep staircase, stop at a brief landing, and then continue upwards. If you want to traverse the outside of the building via the landing, other equally steep staircases serve as pit traps to block you.
At the first floor, your path splits. You can go to the left or right down the covered halls, with windows looking out on the world and in on the terrace, where there once stood a raised wooden pathway but now there are only the stone pegs that held it aloft.
Making my way around the hallway, I came across this well labelled altar which seems to have a hole leading inside of the temple within it. I didn’t try to enter; besides being too small, there’s a good chance it did have a trap, as we’ll see later.
The second tier of the temple is like the first, but strangely devoid of material, and the topmost layer is almost completely empty. This is because of the aforementioned desecration. The Baphuon was originally built as a Hindu temple, but in the 15th century was taken over by Buddhists, who stripped it of the 16 meter tall tower at its peak and tore down much of the black sandstone on the second and third levels, and used them to construct an enormous stone statue of the Buddha on the back side of the temple.
But the temple was trapped. The way that mountain temples were constructed is that a hollow base layer of laterite was constructed, and then covered in black sandstone, which serves to both reinforce and decorate it. Then the interior hollow area was filled with sand. Then the next layer of the mountain was built on top of that, and the process repeated.
When the Buddhists removed the black sandstone from the top layer of the Baphuon to build their statue, they removed the reinforcements holding back the sand. Eventually, the laterite gave way, the sand poured forth, and the statue was destroyed in the ensuing avalanche.
It wasn’t until the 20th century that restoration efforts were taken seriously, and it wasn’t until 2011 that the temple was fully restored. Well, “fully” in a sense: due to Cambodia being Buddhist now, the decision was made to restore the temple with the statue of the Buddha in place, instead of restoring the topmost layers of the temple. The statue is now held in place by hidden metal restraints, keeping it safe from the wrath of its original builders.