What can guests actually do inside the gallery once they're in?

Quite a lot, considering how simple it looks. They can switch between folders if the album has sections, tap the heart to favorite photos they love, use Select Photos for batch actions, and hit "Download all" when they want everything that's theirs. Big albums load in pages — you'll see "Showing 50 of 400 photos" with a load-more control — so the page stays fast even on huge events. It's deliberately sparse: no ads, no clutter, just their photos and a download button.