When I lived in Alabama we had a two story split level house. The front porch ran the length of the house, 12' wide and 4' high. It looked like a solid porch, concrete and brick but it was hollow - you could access it from the back of the closet under the steps in the first story of the house. Very well hidden but perfect for sitting out bad storms (or hiding an army I guess if you were so inclined)
Um what about black widow spiders, brown recluse spiders, mice or snakes? I'd be too afraid to go under a porch! : )
Sounds like a nice thing to have. The person who built it was really thinking ahead to provide access to that area. Most people wouldn't have even thought about it. That's the nice thing about a custom built house, you can do neat little things like that.