Only one day in Edinburgh. What are the top attractions? What’s do-able in only one day?
How did you end up in the Scottish Capital for just 1 day?
My favorite sights were the National Museum of Scotland, Greyfriars (especially if you're a Harry Potter fan), St. Giles Cathedral, and walking up Calton Hill.
I did not feel that Edinburgh Castle was a must-see (and in your case, since your time is limited, I would just stick with seeing the outside of it). Other things you can do are walk the Royal Mile, which is fun, or go to the Royal Botanical Gardens, if you like stuff like that. Eat lunch at Bertie's Proper Fish & Chips.
There are also many fun tours that you could do - Mercat Tours has some very interesting tours and are highly regarded on this forum. https://www.mercattours.com And there are the hop-on-hop-off bus tours that would give you a good overview of the city.
I just got back from Edinburgh 2 days ago and just posted my trip report, so you might pick up some ideas there (scroll down to the end for Edinburgh). https://community.ricksteves.com/travel-forum/scotland/solo-in-scotland-trains-cars-and-ferries-and-a-wee-dram-or-two