Updated for 2020. All images from the official Hilton Odawara Site.
Every year for as long as I have being doing the Santa lists, the Hilton Odawara in Kanagawa have very kindly had a public Santa for at least one day during the Christmas period. They used to offer it daily from early November, but they changed their system a few years ago when more and more Santa Claus visit locations became available around the Kanto plain.
However, from early November paying customers of the restaurant, specifically the Christmas Buffet, can meet Father Christmas and get a photo with him. The public event generally takes place in December. It is usually a free event and they welcome people of all ages.
The front lobby also has a spectacular Christmas train every year and a Christmas Market. Their full Christmas program will be available online from about early October.
Information on the Hilton hotels in Japan in English here: http://www3.hilton.com/en/hotels/japan/hilton-odawara-resort-and-spa-TYOODHI/index.html
From their English site:
DIRECTIONS BY CAR FROM THE HOTEL STAFF
Take the Metropolitan Expressway (Kuko chuou) to the Tomei Expressway Atsugi Interchange. Take Odawara Atsugi Road to the Ishibashi Interchange onto Route 135, then the intersection at Manazuru Road to the Hilton Odawara Resort & Spa.
DIRECTIONS BY TRAIN
Take the Tokyo Monorail to Hamamatsucho, then the JR Yamanote Line to Shinagawa. Take the bullet train to Odawara then free shuttle bus (Mon to Fri, except holidays) to the hotel. Free shuttle is available also from Nebukawa Station daily.
For more Santa events in the greater Tokyo area please see the ultimate Santa Guide.