1) Celtic mythology encompasses the folklore and legends of the Celtic peoples across Europe, particularly in regions like Ireland, Scotland, and Wales. It features deities like Morrigan, Cernunnos, and Brigid, and delves into themes of nature, magic, and the heroic exploits of legendary figures like Cu Chulainn.

2) Matcha, a finely ground powder made from specially grown and processed green tea leaves, is a cherished part of Japanese tea culture. It has a vibrant green color and is known for its earthy and umami flavors. Matcha is prepared by whisking the powder with hot water and is traditionally enjoyed in tea ceremonies. It is also used as a versatile ingredient in desserts, beverages, and even savory dishes, offering a unique and distinctive taste.

3) International relations encompass the study of relationships between nations, including diplomacy, treaties, and foreign policy. It examines the interactions and dynamics among different countries in the global arena.

4) The world's largest particle accelerator, the Large Hadron Collider, is located near Geneva, Switzerland, and spans a circumference of 17 miles (27 kilometers).