Tivoli on Sunday-taxi or walk between Villa d'Este and Villa Adrianna?

That is an hour’s walk, largely exposed as I recall (we had a car). Take a taxi, by all means!

It is way too far, and too hot and exposed. It is very possible that regular (but low Sunday frequency) busses might be running along the main road. You will still have to walk 1/2 mile from the main road to Villa Adrianna, but that is do-able. The main bus starts at Ponte Mammolo in Rome, and runs to Villa d'Este, maybe farther. It returns the opposite way on Via Tiburtina. I am distinguishing these main road busses from a "shuttle" that connects (? haven't taken it) two big sights.

This is a long post, but it will give you some background for more online research:

https://community.ricksteves.com/travel-forum/italy/hadrian-s-villa-annoyances-and-directions#top

Edit: Small clarifications. Note that the bus directions in the link are mostly coming from Rome to Tivoli.

I agree completely with Laurel and Tim.

Too far, too hot, no shade. I wouldn't walk that.

But then again, you have to pry me out of the Villa d'Este with a crowbar. Tell you what. Y'all go on and I'll stay here.

This information is VERY helpful - THANK YOU!!! I agree that a 1 hour walk in the sun is NOT what we want to do.

I would be happy to take a taxi, but it sounded like they are difficult to get. Maybe it will just require persistence and help from a local.
I didn't realize there were 2 different bus companies in Tivoli, I'd only been looking at CORTRAL. I'll dig to try to find the local bus information. Hopefully it runs on Sunday! I keep thinking that surely I'm not the first person who wants to see both sights on a Sunday who isn't with a guided tour!

We took a bus on a Sunday, but unsure what line. Highly recommend Sibilla for lunch.