It is definitely on the lower slopes of Arthur's Seat (as suggested by Skoosh) just across the road from Holyrood Palace. This lovely park in the centre of Edinburgh used to be called the King/Queen's Park depending on who the monarch was. Nowadays it is usually referred to as Holyrood Park.
I have seen many a parade there including "Beating the Retreat" which is a spectacular event with the pipes and drums of the Scottish Regiments. Nowadays I think this happens on the Castle Esplanade. Happy memories although I don't go back quite as far as 1906.
The Argyll & Sutherland Highlanders known as Princess Louise's Own. She was a daughter of Queen Victoria and Colonel In Chief of the Regiment. The regimental museum is in Stirling Castle and well worth a visit if you are ever in Stirling.
What a wonderful photograph to have Lauren. Lucky you.
P.S. Skoosh - Lots of drinking dens up the Royal Mile to "wet their thrapple"