When you start to investigate a particular Internet site, I suggest you begin with these resources.
Domain Dossier Investigate domains and IP addresses. Get registrant information, DNS records, and more—all in one report.
InterNIC Public Information Regarding Internet Domain Name Registration Services
DomainSearch.com Search multiple top level domains at once to see if the domain name is in use. I use it to find the domain name in other top level domains.
Convert Host/Domain Name to IP Address and vice versa Find the IP of a host machine (convert host to IP) or domain name (convert domain name to ip address) or find the name of one of the hosts at an IP address (convert ip address).
Using Traceroute Learn how to use and interpret traceroute results.
Additions thanks to Kirby:
hostcabi.net Provides lot of information, but most importantly, it identifies other users of same Google Analytics account and all the sites using that account.
sitedossier.com Sometimes shows older servers, which is useful when website has upgraded to cloud service or CloudFlare.