In Olympia Washington, there is a building I would like to find. It can be seen from I-5.?

So I regularly travel through Olympia on Interstate 5 and there is a building right near the capital that I would like to find. If you're heading north it is on your right, and if heading south it is on your left. Its about level with the capitol building, maybe a mile off at most. Its a large, brick, four, maybe five story building. It sits down in a low, somewhat marshy looking area. It can be see from the interstate. I vaguely remember someone telling me once it was an old water treatment building. It looks beautiful and has been intriguing me for the last few years. Is there anyone who can help me?