You're standing in an area of Inverness that has seen building, conflict and rebuilding for almost one thousand years.
The first building that stood atop this cliff was a wooden defensive structure, which was said (according to the artistic licence of local tradition) to have been built by Malcolm III of Scotland. This was after he burnt down the castle of Macbeth, following Macbeth's murder of Malcolm's father, Duncan I of Scotland. That castle was supposedly a kilometre to the north-east, in the modern day Crown area, which overlooks a Morrisons Supermarket.
The first stone Inverness Castle was built by David I of Scotland and damaged heavily by Robert the Bruce in 1310. Its replacement was then sacked in the 1429 Siege of Inverness.
Another famous incident involved the governor, one Alexander Gordon, in 1562. He shut the castle gates on Mary, Queen of Scots, which prompted another Siege of Inverness (quite a few of these) in which supporters of the Queen overran the Castle. Gordon was hung after the three day siege for treason and his head displayed for all to see.
There were further sieges in 1649, 1650, 1689, 1715 and 1746. The 1746 edition involved two Indepenent Highland Companies surrendering the Castle to Bonnie Prince Charlie's Jacobite force on the orders of Duncan Forbes, Lord Culloden. The Bonnie Prince then ordered Inverness Castle be blown up to remove it from the chessboard as it were. A story goes that a French sargeant (complete with his poodle) was the one to set off the explosives. He managed to blow himself up in the process, his body clearing the River Ness in the blast. The darker, obviously older curtain wall is a hangover from this particular version of the Castle.
The current red sandstone Castle was designed by architect William Burn and completed in 1836. Burn designed North Leith Parish Church, Blairquhan Castle and The Edinburgh Academy amongst other buildings.
Continuing the Bonnie Prince Charlie theme, the brass statue in front of the Castle is of Flora MacDonald. She secured her place in history by helping the prince escape the Isle of Skye after he fled Culloden. The statue has stood here since 1896. At the time of placing this cache, Flora was still wearing an Inverness Caledonian Thistle scarf that was placed to show her support ahead of the team's Scottish Cup Final appearance (and eventual 2-1 win!) just over three months prior.
A matter of local debate for some time, Inverness Castle isn't actually open to the public due its use as Inverness Sheriff Court. Building plans are underway to rectify that at long last.
Finally, Inverness Castle appeared on the reverse of the £50 bank note circulated by the Royal Bank of Scotland from 2005.
As for the cache, you're on the hunt for a nano container placed with a fine view of the Castle and the River Ness down below. There is a muggle factor here of course, considering it's a city centre cache. Enjoy!