The Dee Wright Observatory at McKenzie Pass is a very special building: shaped like a fortress, it is completely made of volcanic rock. Well, if you look around you, you will see that volcanic rock is abundant, so I guess it was also a logical decision to take this material.
A short interpretive trails gives you some information about the landscape around you. The massive lava field was caused by the eruption of the nearby Belknap Crater, but you can hike through lava for miles and miles, since it is mixed with the lava fields caused by The Three Sisters, too. It is a unique landscape and you might feel like you are on the moon. If you want to enjoy a hike besides the observatory here, notice that you need a wilderness permit for the Central Cascades.
There are restrooms at the observatory – a hint for PCT-long-distance hikers. ;)