Kuro Tamago, or "black egg," is a unique delicacy found in Hakone, Japan. These eggs are hard-boiled in the hot springs of Owakudani Valley, giving them a distinctive black shell due to the sulfur and minerals in the water. Eating one is said to extend your life by seven years, making them a popular treat among visitors. The eggs are typically sold in sets and are often enjoyed as a snack or souvenir. Their striking appearance and the legend surrounding them attract many tourists, contributing to the local economy and enhancing the cultural experience of visiting Hakone.