"Good nose," Michael said, heading straight for the stairs. "I think I have some idea where I'd have put it if I had been Remus. Someplace that not even Kate knows exists." He stopped and looked up. "Look up, you two. The house has two floors, a basement and an attic. This library makes use of all that. This floor and two more floors above you and one below you. I'm guessing it will be downstairs--with some of Robert's other secrets." He used the spiral staircase and descended down it fairly quickly, uttering an incantation to turn on the lights as he went down to the cellar.
It was the largest potions lab that Michael had ever seen in his extensive career, with thousands of bottles on the walls. Some held insects and some held potions, and some held potions ingredients. Other shelves held all sorts of potionmaking supplies. "I daresay I don't think you'll see a larger lab anywhere in the world," Michael said. "But let us to go the part that Robert's kept from the women in his life, shall we?" He went to a back wall, flicked his wand at a huge stone bookcase and aimed his wand and fired a spell at it. the bookcase moved easily out of the way to display a thick ancient looking wooden door. Michael went over to the door and the carvings on it and began assembling the odd abstract looking carving, slowly and with much thought. It began to take shape as a landscape carved into the wood. Once completed, the door opened easily to Michael.
"Come in and be very careful. These things are all loaded." He turned on a light and it showed enough muggle weapons to equip a large army. Guns, knives, spears, crossbows, daggers, maces, shields, swords...if it was a weapon, it was here. An cabinet after cabinet of ammunition.
"Robert and Remus liked weapons. They started a collection when they were kids. It...sort of grew a bit. And when Kate got pregnant, Remus and Robert enchanted it to be far too difficult for a child to accidently get into. If I were Remus, I'd have put the safe in here. No one but Robert even knew it existed until fairly recently when he told me about it. And I would trust it would be a wizarding safe and not look like any sort of ordinary muggle safe. Look for anything that looks like a box, a chest, a larger piece of stone block than the others...or an odd crack in the mortar in the regular sized blocks, something rather unusual and very very well hidden. Remember, Robert knows this room like the back of his hand, and he doesn't know where the safe was either. Only that Remus had one somewhere on this planet. I think he'd just given up searching for it."