Returning to the magic train?

So I finished a bit into the game already.. and then I realized I was missing a treasure from Twilight Town. I remember that there was a treasure chest I missed back at Mickey's teacher's tower (forgot his name).. the one I took the magical train to get there with.. is there any way to get back there?

I went back to the station plaza, but the train isn't there....

Maybe I will go there later in the story again? Help please! D:

It becomes available again later. I'm not quite sure when exactly it is there, but towards the end it's back. The tower is crawling with Nobodies, though.

At the end it's available for sure.

Once you find the second Twilight Town and the World that Never Was, it opens again.