Stage 1 - Glen Mark
Look for the Invermark Estate plaque and then subtract the characters in the 4th word of the title from the 1st word of the title to obtain the coordinate of A.
Glen Mark is a glen in northern Angus through which the Water of Mark flows. Near the mouth of the glen, at Auchronie, the Water of Mark is joined by the Water of Lee from Loch Lee to become the River North Esk. This flows through Glen Esk, one of the Five Glens of Angus.
Stage 2 - Queen's Well
Count the number of lines of text on the plaque and then divide this number by 3 to obtain the coordinate of X.
Queen Victoria and her consort Prince Albert purchased Balmoral Castle and delighted in travelling the mountain routes in the area. In 1861 they rode the 15 miles (24 km) from Balmoral to Glen Mark and met with Lord Dalhousie beside an artesian well. Here they were refreshed by the spring water before continuing to Invermark Lodge where they stayed overnight. To commemorate the visit, Lord Dalhousie erected a monument in the shape of a royal crown over the well.
Stage 3 - Cairn
Just South of the small cairn you will find the cache tucked away. Inside are the coordinates of B.
Mount Keen (Gaelic: Monadh Caoin) is a 3,081 ft (939 m) high mountain in Angus and the most easterly Munro. It can be accessed from several directions, South from Glen Mark, North from Glen Tanar, and East to Braid Cairn. It is a moderate walk which is most popularly started by mountain bike, riding through the native Caledonian pine forest of Glen Tanar from Aboyne. On a good day, the Cairngorms, especially Lochnagar, can be seen. The summit is marked by a trig point.
Stage 4 - Final Leg
Off to the right hand side of the path you will find the cache tucked away. Inside are the coordinates of Y and the hint to find the final container.
You are now at an elevation of 2630 ft (802 m). Have a quick rest here before the final push to the top.
Final Location
The cache can be found at N56 58.AB W002 58.XY.
Thanks to vgiorgio for kindly donating the very apt final container. He was very Keen to do so.