ELI5: Explain Like I'm 5

Great dolmen of Dwasieden

Okay, imagine a big stone house that is older than your grandpa's grandpa's grandpa. It is called the Great Dolmen of Dwasieden. This house is made out of enormous rocks that were put together a very, very long time ago. It is like a big puzzle that was solved by very smart people with big muscles.
People used to go to this house to do important things, like ceremonies or meetings. Inside, there is a small room made out of even more big stones. It is very dark inside because there are no windows to let the light in. There are also holes in the ceiling where people could maybe put things like fire or light, but we don't really know for sure because it was so long ago.
So, this big stone house is really cool because it is very old and very big, and it makes us wonder how people could do something like this without big machines or technology.