Safari's webhistory files
Webhistory files are used by Spotlight since macOS 10.5 "Leopard". They ley you to search your past browsing as they contain all the text from the visited pages, but not the images.
You can extract the text, but it is simpler to double click the file to view its contents in Safari.
They can also be opened directly with TextEdit ot TextMate, but you may need to tell that it is in UTF-16 format.
Safari's web history files are now (2017) SQLite3 databases which you can dump with File Juicer (or for advanced users - via the Terminal).
You can of course view and search it in Safari with the History Menu.