I would like to buy www.caves.com but it seems that it's owned and there is a "search engine" there. How do I contact the site owners and buy this domain?
If there is no email address listed on the website you will need to search for caves.com on http://www.whois.net to see who owns the site. Whois will give you all of the information it can about who owns the site. Some registrars allow for private ownership and basically don't show any information about the site you searched for.
I did a quick check and in this case it looks like it is registered at MONIKER ONLINE SERVICES, INC. Unfortunately, it looks like the account is private so that is all of the info there is about the site. You probably will not be able to contact the site owners.
Also, it looks like caves.com is using a pretty common spam/advertising template so chances are they are just making money off of the domain and not doing anything else.