There are times when you will want to link directly to a specialty in order to immediately filter the content displayed on page load. To do this, simply link to:
https://website.com?sp=catID,catID2
The "catID" for any category can be determined by visiting the category manager in the admin console and clicking the EXPORT CSV button atop the page. The resulting spreadsheet will give you the catID's for every category you have in the system.