Nara's Hannyaji Temple is often referred to as the cosmos temple for good reason - there are approximately 150,000 cosmos flowers here, encompassing 30 different types. The best time to catch them in bloom is around the first week of October through until mid-November, but do check their official website for updates - they update their blog with seasonal flower information regularly, so you'll know when the cosmos are at their best.
Along with the beautiful flowers to enjoy, the temple is a fascinating one for history buffs - it dates back to the year 629.
Adult admission to the temple grounds is priced at 500 yen.