need a return ticket to the US to travel in Europe?

I have traveled a lot in Europe and have never been asked this. In fact, even in other parts of the world, haven't needed to show proof of onward journey with one exception - Japan.

20 years ago, I was asked to show my return ticket to Immigration at Heathrow. I did not have a return ticket as I was travelling on a special youth fare where the ticket could only be purchased 72 hours before departure. I explained this to the Immigration Officer and then was asked to show all my money and credit card. Once the Officer was satisfied that I had funds to return home, he admitted me.

You may want to check what your ticket options are. You may still find it more economical to buy a return ticket that allows you to change the return date.

I've flown into Italy and Greece. The matter never came up.

They have the right to ask and will if they think you might overstay your visa, or try to get illegal work, or not have enough money to get home.

As long as you have a couple of credit cards and can prove you can pay your way while in their country, you should be fine.

When I traveled through Heathrow last May, I was asked how long I intended to be in the UK. I replied that I was just changing airports (to Stansted) and then would be leaving. I was asked to show my flight confirmation for my flight out of the UK, though I didn't ask why.

I've never been asked at any airport to show a return ticket - not at Heathrow, Gatwick, Dublin, Madrid, or Rome. However, when I was going back to London from Paris via the channel tunnel, they wanted to see my return ticket to the U.S. Random.

When I went to Australia, they had a requirement that you have a return ticket and the equivalent of 20 Australian dollars (for the exit tax) to be admitted to the country. I haven't seen that anywhere else but I expect they have some rules about vagrancy. You need to show you are a tourist and not a penniless would-be immigrant. Each country will have a website that explains their current rules.