Holyrood is one of the Queen's official residences -- owned by the Crown, as opposed to Balmoral Castle, which is owned by the Queen. We couldn't go last week, since she makes an official visit to Scotland in early July each year, for official functions such as opening the Scottish Parliament, and the place is closed to the public then. The palace dates back to 1501 and the reign of James IV of Scotland; he built it adjacent to the older (12th century) Holyrood Abbey. Like most historical sites in the UK, it (a) has a lot of history and (b) has been extended and renovated many times.
Here is the obligatory I-was-there photo in the forecourt in front of a waterless fountain.
We weren't allowed to take pictures inside, but the place is beautiful. The first dozen rooms on the tour are in active use when the Queen is in residence. It includes a massive hall lined with portraits of former Scottish monarchs, both historical and legendary (such as King Fergus supposedly around 330 BC). The last few on the tour are set up a they would have been in the time of Mary, Queen of Scots.
After the tour, we briefly looked at the ruins of the old abbey:
We then headed a bit south to climb to Arthur's Seat, the highest point of a volcanic extrusion right in the middle of Edinburgh. This is the view of the Salisbury Crags from the Scottish Parliament; Arthur's Seat is sort of hidden behind it from this angle.
Edit: here is Margaret's blog about the same day.