The tours featured on this website have used different software to create their tours and experiences. While most are self explanatory, there are a couple that can be quite fiddly. The main fiddly tours are the museums that are featured on the Google Arts and Culture website. If you find that a tour is featured on GAC, look out for this little guy near the top right of the screen; that'll take you to the tour.
Alternatively, scroll a little further down the page and you'll find the 'museum views'. The Rijksmuseum in Amsterdam has been used in the example below.
How are the tours created?
I'm no expert in the 360° photography field, but in the simplest way, the process involves taking multiple panoramic photographs and 'stitching' them together to create an experience that flows.
How to find more
Some landmarks or places of interest may have a Streetview option that I haven't stumbled across. Some of the tours on this website are based on Streetview; in fact, quite a lot are!
Google search - 'virtual tour'
If you're going to start looking, you may as well hit the keywords. You may have even found this website using those keywords. A lot of the tours on this website were found using 'virtual tour of... place name'.
If you find any tours that aren't on this website, but think they should be, please let me know by dropping me an email at email@example.com