The gateway to the Izu Peninsula is Atami. Most Japanese travelers make it no farther into the peninsula than this town on Sagami Bay, so Atami itself has a fair number of hotels and traditional inns. Although Atami fell on hard times after the economic bubble burst, it has recently undergone a massive revitalization and is once again a lively tourist town. The city also has frequent firework shows over the bay. They are only 30 minutes long, but the display over the water is stunning nonetheless.
When you arrive, collect a map from the Atami Information Center at the train station.