A quick question

This is something I am having a bit of trouble with. Recently I watched the movie Pokemon Heroes and am planning to maybe write some series, which part of it would be based in Alto Mare. My question is how do you get into the secret garden? From the movie, it looked as simple as entering the museum and leaving through the back exit. And are there other houses there other than Bianca and Lorenzo's?

They based of their design from Venice Italy, so you could work off that, as I assume they have plenty of houses there (even if they weren't shown). I think too, that you can be pretty liberal in terms of the entrance and exits. Was there two or three exits?

The three I can recall is the one the old man came through (perhaps in his house?) we don't see him coming back but he does make it out somewhere.

The water (when the Latios goes swimming)

And the wall that Ash stumbles through

You could however excuse it to be magic or some kind of power, and up to either human or pokemon to create a new entrance.

Hope that helps. :)