There are uniquely named forges located in each race's home city that are used for cultural blacksmithing. Humans have 2 home cities, so there are 2 different named forges available to them: the Antonican Forge and the Royal Qeynos Forge. When you open the forge it won't just say "Forge" like most forges do, it'll say the actual name of the forge so you'll know if it's correct or not. Here's the wiki page on forge locations to help you find it:
https://wiki.project1999.com/Forge#Freeport
p.s. if you are playing on the Green server, then cultural recipes are not available yet.