I took someone's suggestion and decided to try the day rooms after I completed security screening at Narita. They offer two types of rooms: one without a bed and one with a bed.

I had a late flight and had been out walking all day, and did not want to spend another ten hours flying back home sweaty from the humid September climate.

The day rooms are clean and comfortable. I took a shower and changed clothes before I headed to my gate for my departure.

The day rooms are located close to departure gate 27 or 28. The dayrooms are 1500 Yen per hour. The shower rooms ( without bed) are 1000 Yen per hour.

And, surprisingly, the airport was air-conditioned while I was waiting to board my flight.