The palace was the ancient Roman version of the Aaron Spelling mansion--sprawling and flashy. From thecolosseum.net:
The area of the property was 985 feet long by 295 feet in width or depth. Among the other things there was an amphitheatre, a market, and bath-gymnasium complex, served by an aqueduct 75 Km (50 miles) long. Baths were served by a flow of both salted water and sulphurous one from the Albulae springs. Upon the Caelian Hill there were beautiful gardens, zoos, woods and parks where cattle roamed . There were hundreds of statues, grottoes, nymphaeums, porticoes painted with romantic landscapes; multiple waterfalls flowed all over. The lake - where the Colosseum was later built - was surrounded by woods and fake sea villages, and it was so big that ships could manoeuvre in it. The rooms of the palace were decorated with rare stones and mother of pearl; in the banquet rooms the guests were inundated by flowers and perfumes from the ivory ceilings (R. Lanciani, Rovine...). One of the most famous of these rooms featured a circular roof painted with the stars and the planets, that revolved mechanically imitating the movement of the stars.
The Golden Palace, or Domus Aurea, as it is also known, was one of the more obscure and enjoyable sites I remember touring in the city. It was right when I was leaving Rome--I went with my stepmother and sister, pitching it to them as something few tourists bother to visit. (I let them go to the Vatican on their own--after dealing with the crowds in the Sistine Chapel, I wasn't eager to do it again.) I seem to remember the guides saying that after Nero's death the emperor Vespasian actually had it covered up with dirt to erase all traces of Nero's profligacy. I can't find a reliable source for this online, but I like the idea of an entire palace sealed up for thousands of years. At any rate, the structure is completely underground (quite near where I lived in Rome, in a much more humble abode), and they've only excavated a small percentage of it, even though its existence has been known of since the Renaissance. Raphael and other artists used to rappel down into the darkened rooms to take a gander at the wall paintings.
It's quite an eerie feeling to head into the cave-like rooms that are open, and even in the height of summer a jacket or scarf is a good idea as it can get really chilly. The rare stones and mother of pearl are long-gone, but some of the wall paintings still exist, and the scale and size of the rooms offer a sense of the building's grandeur.
