Since there is no outside concrete staircase to get to the 2nd floor I'm guessing the entrance/exit highlighted below will be the route up or down:
View attachment 16838
and while the main 1st floor area looks big/spacious that 2nd floor feels really tight:
View attachment 16839
Finally I'm curious what is going on here, seemingly for the interactive games but looks like another turret like on Bowsers castle but with it's own flag pole:
View attachment 16840