Daibosatsu is a mountain in Enzan. It is a good day hike, and with crampons and other appropriate gear it can be climbed even during winter. It is also easily accessible via public transportation, making it somewhat busy on weekends and holidays.
To get to the trailhead, take a train to Enzan Station and then take the bus from the station for about thirty minutes until you reach the entrance (the stop is labeled 大菩薩峠登山口). The bus costs a flat 300 yen no matter where you get on or off at. The timetable can be found here.
Daibosatsu is famous for containing a popular pass on the historic Tokaido route.