The Otherworld:
The ancient Celts believed in an Otherworld. The Otherworld was the home of many gods and goddess. It was a place of joy, where feasts were always happening. The Otherworld was NOT a heaven. It was NOT a reward for doing something good on earth. The Celts believed that everyone entered the Otherworld when they died.
Celtic Tombs:
Like the ancient Egyptians, the ancient Celts wanted their dead to have nice things with them. They wanted them to have food for the trip. They buried their dead in tombs.
Their tombs were not huge things like the Egyptian pyramids. But they were the size of a large room. The walls were decorated with drawings of earth gods, sun gods, various spirits, and scenes of battle and daily life.
They never placed living people or animals inside a tomb. Instead, they tucked little figures of people cooking and hunting. Occasionally, they placed life-sized things into a tomb. One tomb was found with a full size four-wheel wagon in it, and a full size bronze kettle for cooking.
Waterfalls were one of the many doorways to the Otherworld:
Natural waterfalls, especially small ones, were believed to have healing power. To the ancient Celts, they were entrances to the Otherworld. Gifts were left by waterfalls for the gods. Some gifts were even tossed down wells or into springs.
If you were injured, you might place something in a stream to help you heal. For example, if your leg was injured, you might carve a wooden leg and place it in a stream. It did not always work, but the Celts remained great believers anyway in the power of the little spirits and gods whom they believed lived in streams and ponds and waterfalls.
The ancient Celts believed in many gods and goddesses.
The ancient Celts believed that every tree, every bush, every flower, every everything had a little deity living in it. Some of their gods and goddesses were extremely powerful. But most were little deities.
The ancient Celts did not worship their gods. They did not go to church. Instead, they left little offerings all over the place. Each fine had their own special little deities. Each clan had theirs as well.
Unlike the ancient Greeks, the gods of the ancient Celts did not trouble themselves with the affairs of men, unless they were asked to do so.
Sacred animals:
The Celts believed in omens. Birds, especially, were believed to be able to carry messages between the living world and the Otherworld. Many animals were given special powers that could only be understood by a Celtic priest - the druids. Some animals were hunted for food. Hunting wild boar was considered a great sport.