It's not just BIG, it's H U G E!! - Come see for yourself. But beware of muggles, there's an excellent fish restaurant adjacent (www.forellenwirt.com; closed Mondays and Tuesdays).
Bring your own pen, Route67
p.s. The true reason for this cache might be the restaurant, as you will - hopefully - understand when you eat there. Try the "Mühlviertler Forelle" with bacon and onions!