Newgrange

Last Tuesday we took a day trip to Knowth and Newgrange. They're about an hour to the north of Dublin and are Passage tombs built on hilltops that pre-date the pyramids by about 500 years and stonehenge by 1000 years.
The passage that runs through Newgrange was designed so that during the winter solstace (the shortest day of the year) the passage would be in perfect alignment with the rising of the sun and the inner chamber, which is normally pitch black, is fully illuminated by sunlight.
The outside of the tombs are surrounded by huge rocks that have come from as far as 80km away and are carved with neolithic art (new stone age).
Newgrange is actually the oldest surviving man made structure on earth.