From Tokyo
Take the JR's (Japan Railways) L Express "Odoriko". You can also take the "Super View Odoriko", which is 200-300 yen more expensive.

■Tokyo Station to Atami
Using JR's L Express "Odoriko"
Frequency: four trains per day
Time Required: 1 hr 20 min
Cost: Requires a regular train ticket (1890 yen) and an express supplement (2180 yen)

■Using Tokaido Bullet Train "Kodama"
Frequency: two per day
Time Required: about 52 minutes
Cost: Regular train ticket (1890 yen) plus express supplement (2190 yen)

■Using Odakyu Line, JR Line and Izu Express
Shinjuku-Odakyu Romance Car (Express Ticket 850 yen plus seat reservation supplement 870 yen, 1 hr 10 min) -> Odawara JR (400 yen, 20 mins) -> Atami

■Shinjuku - Odawara Station
Frequency: 2 to 4 per hr
Time Required: 1 hr 7 to 27 min
Cost: Regular train ticket (850 yen) plus express supplement (870 yen)

■Odawara Station -Atami Station
Frequency: 3 to 5 per hr
Time Required: 20 min
Cost: 400 yen

From Osaka
Shin-Osaka, Nagoya Station - Atami Station
Frequency: 1 to 2 per hr