Question : how to find out what web site are hosted in an IP address

Given an public IP address, it is possible to find out what web site is using this public IP address?

Answer : how to find out what web site are hosted in an IP address

well, that's not what your original question asked. you're talking about virtual hosts.

try 3d traceroute. here's an excerpt from the user guide:

d3tr -h2h   Converts the hostname into a IP-adress and the IP-adress back into a hostname. Useful to detect virtual hosts.