Hate to do this but ... Knowth: no one really knows what it looked like as it was re-used and re-used over and over again. There was a fortification ditch dug inside the kerb, completely destroying the cairn walls/facia. A fort was built on the top. Souterrains were dug into the sides. Basically it's a mess.

The only bits of Knowth/Newgrange that can be truly judged are the kerbs and the insides, i.e. the passage/chambers themselves and internal cairn structure. Now, the passage and chamber at Newgrange are undoubtedly amazing pieces of advanced engineering. Not only in the amazing alignment and roof box set up, but in structure. The use of corbels and lintels and a great knowledge of how to cantilever structures for strength and stability.

As a side note: Apparently you need modern surveying equipment to differentiate between the sun's position for the four days either side of the Solstice, so the alignment of the passage could have easily been done by eye and not through any special advanced maths or astronomical calculations. So the alignment isn't necessarily that amazing, other than the fact that they thought it significant. What is amazing, and totally demolishes the neolithic 'caveman' genre, is the manhours and organisation it took 5500 years ago.