SentrySafe Secret In-floor Safe
This funky cylindrical thing is actually a safe. You install the Sentry Safe in your floor, and would-be thieves are supposed to walk right over it without ever knowing it’s there. It can be installed in wood or concrete, and it’s designed to lie flush with the floor. Toss a rug over it, and it disappears. On the off-chance that someone does find it, there’s a 12-gauge steel body with a heavy die-cast aluminum door to protect your goodies.
Since the safe is waterproof as well, you can install it in a basement or ground level room without worrying that flooding will destroy your documents or whatever other important items you keep inside. I found the in-floor safe at Home Depot where it sells for $119.