I've seen, what I was told, was an antique wood/iron vault. Once upon a time a train station, now a house. I think it was white oak. Wood planks, they were about 6x6's, laminated with flat bars of iron. Kind of like plywood. Oak/iron/oak/iron/etc. Imagine a log cabin with iron chinking. Presumably it was all spiked together. That would be a bugger to break into because for the most part what cuts wood doesn't cut metal very well and vice versa. It would also be reasonably fire resistant. I think old west prison doors used a similar concept. I've thought about recreating something like that just because it would look so cool.