Lupercalia is a Roman ritual of purification and fertility dating from such an ancient time that even the Romans of the first century BCE had forgotten its origin and to which Gods it was dedicated and even the meaning of some of its symbolism. (Contrary to Z Budapest's statements, it was not known whether it was to Faunus and in fact I think it may have been sacred to the more ancient founding Goddess, Rumina, the She-Wolf of Rome.) Central to the ritual is the lustration (light flogging) with a goat skin scourge (see, Gardner didn't invent it). This was often accompanied by much rowdiness and horse-play. The purpose was the purification of the people from curses, bad luck and infertility. The ritual is performed on February 15. The name of the month comes from the februa, anything used in purifying including wool (used for cleaning), brooms, pine boughs (which make the air sweet and pure), etc.
The rite began in the cave of the She-Wolf in the city of Rome where legend had it that the founders of the city, Romulus and Remus, had been suckled by the wolf before they were found by a shepherd. The sacred fig tree grew in front of the cave. Vestals brought to the site of the sacrifice the sacred cakes made from the first ears of the last years grain harvest. Two naked young men presided over the sacrifice of a dog and a goat. With the bloody knife, their foreheads were smeared with blood, then wiped clean with wool dipped in milk. The young men laughed and girded themselves in the skin of the sacrificed goat. Much feasting followed. Finally, using strips of the goat skin, the young men ran, each leading a group of priests, around the base of the hills of Rome, around the ancient sacred boundary of the old city called the pomarium. During this run, the women of the city would vie for the opportunity to be scourged by the young men as they ran by, some baring their flesh to get the best results of the fertility blessing (you can see why the Christian church tried so hard to get this ritual banned, but it was so popular that it continued for quite some time under the new regime.)
Except for the intrusion of foreign cults, this was the only Roman ritual where a goat was sacrificed. Dogs were only offered to Robigus (a guardian associated with crops), the Lares Praestites (the guardians of community), and Mana Genata (ancestral guardians).
Because of the cave, the fig tree, the milk, and such, I suspect the very oldest forms of this rite honored a Goddess. Unlike some of the other Roman rites like the October Horse sacrifice, there is no other Indo-European equivalent in Vedic, Scandinavian, Irish, or Indo-Iranian traditions.
With modifications, the Temple of Pomona performed Lupercalias and has a great time.