This is a topic for anyone who's ever spent slightly too much time seeing how far you can get on the banks of Whisper Bridge, or trying to get round the side of Narukami Shrine, or checking the locked doors in Rougetsu Hall wondering if there's some kind of sidequest to get them open. I know that as far as the game is concerned, these are basically the same as walls, and if we can't get in it's because there's nothing to see, but I do sometimes wish there was a bit more freedom to explore, and not as many paths blocked by two inches of grass. It can't be just me, right?
For example, I've always wished there were a way to get out onto that walkway on the outside of the Engraving Shrine, where the vanishing ghost of the Engraver appears when you're walking over the roof. I wondered if it might have been the intended location of the beginning cutscene where Reika walks towards you along a curtained passage with lots of windows that never appears anywhere else in the game. (Although I will say, the fact that nearly every hidden door and sealed room in FF3 can eventually be opened is a very big reason why it's my favourite.)
I also wanted to get into the room behind the reception in Rougetsu Hall, and up onto the second floor where there's a window that the hidden nurse ghost is looking down from. There's Iori and Yoriko's rooms, obviously. That door leading from the Meditation Cave makes me curious, too, and I really wish some of the doors to the outside of the lighthouse worked.
I'd also really like to have seen what Kiryu House had in place of Tachibana House's Row of Tatami Rooms, but that section of the house is all collapsed and boarded up.
And last but not least, the entirety of the Old House in Spirit Camera. GET ME OFF THESE RAILS, I WANT TO LOOK AROUND. D: