Can someone tell me what this dream means?

ok. i have the re occurring dream that i am at the beach with the friend playing in the water and the ntheres a huge tidal wave. then, me and my friend run but then she just disappears. then on the beach, there is a huge castle and i run into it and right when i get into the castle, everything is destroyed and i was safe, when i got to the top of the castle,i looked over the beach and everything was serene and beautiful and the beach looked like it was just the same and normal. can someone tell me what this means?