Never heard of the festival here some quick information:

The Hounen festival at Tagata shrine is one of the most famous (or infamous?) festivals in Japan. Amongst foreigners visiting Aichi Prefecture it is frequently referred to as the “penis shrine”, or “Japanese penis festival”, primarily due to the ancient Hounen Matsuri (a festival celebrating fertility and renewal), which is held here every March 15th.

The shrine is located in Tagata Jinja north of Nagoya. The festival is held every year to ensure a good harvest and promote baby making.