jib's idea sounds good if you've got the energy. If you're tired, it won't be such a bad idea to just spend your short time at Hotel Nikko NRT. I always enjoy the hotel, and time goes fast when I'm there. Just catch the hotel shuttle bus from NRT to the hotel. Runs fairly often (like q30min or so) and takes just ~10min. Love their Chinese restaurant... they have all-you-can-eat option, too. There's a 24hr konbini in the lobby (Lawson), and you'll end up hanging out there quite a bit. It's your chance to try all different sorts of Jpn sweets, snacks and beverages. Just a few minutes walk out the lobby is another konbini... a much larger one. In the morning, the breakfast buffet at their restaurant Serena is great and it's the type of stuff you don't see in US... they have all the usual Jpn/Western mix, plus their croissants are top-notch and the curry is delicious.