Google has recently launched a feature called "teleporting" *. It means that when you search for specific site, another search box might open within the search results.
Here is an example from a Google search for
hostelworld:
If you type a search query into the secondary search box, you get what is called a Google "site:" query, which is a regular search within a single site:
Hostelworld is the only hostel booking engine that seems to have this "teleporting" feature. If you type in hostelbookers, hostelsclub, or hostels, there won't be a secondary search box. I haven't seen too many search results with this feature. Another keyword that triggers this behavior that I've seen mentioned in Internet marketing blogs is
virgin holidays.
*further reading and reference: googleblog.blogspot.com/2008/03/search-within-site-tale-of.html