It really depends on your interests, in Kanto Region, we have cities like Tokyo, Yokohama and also traditional districts like Kamakura, Kawagoe, Nikko, Sawara, etc. For nature, Minakami, hiking in mountains in Chiba or Ibaraki (like Mt. Tsukubasan or Nokogiri-yama), we also have beach in Kujukuri-hama and Shonan.
Kanto is huge! It differs depending on your interested. If you want to see the old streets and atmosphere of Edo, then Kawagoe would be suitable.
Kanagawa is also an interesting place to visit! Kanagawa has many sightseeing places; Museum, Temple, China Town, beach, park, Onsen... etc.. You will never get bored there!