If you decide a guided tour for Temples and Shrines in Nikko city in the first day, the next day I strongly recommend a walking tour that you can enjoy a relax sightseeing of natural landscapes such as Lake Chuzenji-ko, Kegon-no-taki waterfall, Ryuzu-no-taki waterfall, Yu-taki waterfall, Senjo-ga-hara, and mountains. If you contract a full day guided tour, in the next day You can hire a guide at fee of ¥5000. Because guide points are not so many and just guide a walking course safely. You can take a walk just following your bent.
We prepare three options depending on your feet strength or matter of your liking. Buy a Yumoto-onsen free pass (¥3000), or a Senjo-ga-hara free pass (¥2650) that allow you to ride on and off any bus-stops. You can take a bus at any bus-stop near by your hotel for the entrance of Yutaki or Senjo-ga-hara or Akanuma. You can watch all of the scenery above and enjoy walking in a deep Nikko field. I think that a half day wandering is not enough to enjoy the inner part of Nikko. I think it is possible for them to trip themselves. However, they like to hire a guide even they get information below, I can help them.
National Scenery spots
You can enjoy natural beauty during 5 hours to 7 hours. But I'm not sure how you like hiking, so I'm offering three options as followed. About three hours walk, two hours walk and one hour walk.
Option 1 (If you are a good walker, recommend 3 hour walk)
◯Near by Hotel→◯Entrance of Yutaki → (2-hour walk in Senjo-ga-hara) → ◯Aka-numa → (lunch) → (1-hour walk beside a river) → (watch Ryuzu-no-taki) → ◯Ryuzu-no-taki→ ◯Entrance of kegon-no-taki →( watch Kegon-no-taki) → ◯Entrance of kegon-no-taki → ◯Near by Hotel
Option 2 (If you are middle class walker, cut off 1 hour walk)
◯Hotel→◯Entrance of Yutaki → (2-hour walk in Senjo-ga-hara) → ◯Aka-numa → (lunch) → (watch Ryuzu-no-taki) → ◯Ryuzu-no-taki→ ◯Entrance of kegon-no-taki→( watch Kegon-no-taki) → ◯Entrance of kegon-no-taki → ◯Near by Hotel
Option 3 (If they won't walk so long, only 1-hour walk)
◯Near by Hotel → ◯Akanuma → (1-hour walk beside a rive) → (watch Ryuzu-no-taki) → (lunch) → ◯Ryuzu-no-taki → Entrance of kegon-no-taki →( watch Kegon-no-taki) → ◯Entrance of kegon-no-taki →Near by Hotel
◯ sign is bus stop : check a bus's time table. Even you miss some bus, it is no problem because there are many buses followed it about each 30 minutes in the daytime. But you have check the last bus of the day.
Pictures where we are going to see
Mt. Nantai-san and Lake Chuzenji-ko
Even in Japanese but you can get some information. And click here, then you can jamp to a site of this map. You can see the enlarged map at the bottom. A Red line is a route I recommended.