If I download the Rick Steves app ahead of time, will I be able to use it at the Acropolis or does it require cellular data or a connection to Acropolis WiFi?
Assuming you want the audio tour--You will not need wifi or data if you download the tour ahead of time. First get the app, then download the specific tour you want. It will show up in Your Playlist. You can listen to it any time without wifi or data.
Have fun!
The simple plan would be to download it and try it at home. Turn on airplane mode and see if you can get it.
The audio tours are .mp3 files, just like most music files are these days.
Even without the app, if you simply download the .mp3 file, you can play it
with any music player and listen while offline.
The app is helpful if you are downloading multiple files to keep track of things,
but even then, if you download multiple files and rename them to suit your
needs, the app isn't really needed.