What's inside...?

There was a story about dreams, so I'll share a dream story too. It wasn't dramatic or exciting, just my heart pounding💧. In my dream, I was inside a very large temple. I was standing in the middle of a long corridor. I was walking, thinking, "Is this really a temple?" when suddenly, in the middle of the corridor, I saw a large, round coffin, the kind I'd only seen in dramas. Naturally, I was surprised. "A c-coffin!?" While I was surprised, three shrine maidens in white and red costumes appeared from a room... I was surprised again. "Why are there shrine maidens in a temple!?" Come to think of it, their costumes were slightly different, with gold ornaments. The three shrine maidens circled around the coffin, dancing, and then reached for the lid, trying to open it. Seeing this, I was stunned and thought, "Eh!? They're opening it? ⊙.☉!? Opening the coffin!?" I was flustered. "Stop!! Don't open it!!" I screamed in my mind and then woke up. I still don't understand why I had such a dream. That coffin is also a mystery. What was inside? And the shrine maidens in the temple are also a mystery.