Hi,
i was wondering if a page from my website (website.com/thesecretpage) can be found. If it can be in a sitemap in the html or something.
I mean if i don’t share it someone can know there is this page on my website?
There are many ways for someone to find out “that” page on your website via using one or all from below:
- SEO tools like Screaming Frog, Ahrefs, SEMrush etc.
- Website downloaders like HTTrack or websitedownloader.io
- Web scrapers like Octoparse
These tools are basically crawlers that serve different needs that behave more or less similar to discovering content you have online.
To make your page undiscoverable that’s a different story, either put it behind a password, noindex it, serve the website behind a firewall that can have limited access to certain IP’s or don’t put it online at all 
If a page is not in linked to, and it is not in a sitemap then it is, for all intents and purposes, invisible. Only those that were given the URI would be able to see it / be aware of its presence. The same goes for bots/crawlers. Of course, if you shared it with one person, they could share it with others. Security through obscurity is not a good plan to secure a resource.
Thanks, i thought the same.
I would like to make a little website where you need to find clues and type the answer in the url to access a success page.
The best things is password protection i guess?