The river at this point, after some hundred yards of rapid, makes a sudden turn round a rocky angle, and plunges madly into the pool itself. Very deep water lies at the head of it, but deeper still further down on the east side, where a portion of the stream flicks back again in a swift dark backwater towards the top of the pool again. It is fishable only from the western bank, for to the east, above this backwater, a great wall of black and basaltic rock, heaved up no doubt by some fault in strata, rises sheer from the river to the height of some sixty feet. It is in fact nearly precipitous on both sides, heavily serrated at the top, and of so curious a thinness, that at about the middle of it where a fissure breaks its topmost edge, and some twenty feet from the top, there exists a long hole, a sort of lancet window, one would say, right through the rock, so that a slit of daylight can be seen through it. Since, therefore, no one would care to cast his line standing perched on that razor-edged eminence, the pool must needs be fished from the western bank. A decent fly, however, will cover it all. It is on the western bank that there stand the remains of that which gave its title to the pool, namely, the ruins of a Pict castle, built out of rough and scarcely hewn masonry, unmortared but on a certain large and impressive scale, and in a very well-preserved condition considering its extreme antiquity. It is circular in shape and measures some twenty yards of diameter in its internal span. A staircase of large blocks with a rise of at least a foot leads up to the main gate, and opposite this on the side towards the river is another smaller postern through which down a rather hazardously steep slope a scrambling path, where progress demands both caution and activity, conducts to the head of the pool which lies immediately beneath it. A gate-chamber still roofed over exists in the solid wall: inside there are foundation indications of three rooms, and in the centre of all a very deep hole, probably a well. Finally, just outside the postern leading to the river is a small artificially levelled platform, some twenty feet across, as if made to support some super-incumbent edifice. Certain stone slabs and blocks are dispersed over it.