This is an interesting trip, most un-Lancaster like, that goes almost nowhere. The Magic Roundabout Series takes off (literally!) from the high level route in Lancaster Hole near Stake Pot, and ascends the impressive 43-metre Arson Shaft, before following a stream down to the Master Cave via the well-named, 23-metre Aquarius Pot, arriving some 20 metres horizontally and 20 metres vertically from where it starts. It requires reasonably dry conditions as Aquarius Pot can become impassable (it's only bolted for a pull-through), and much of the passage below can fill up.
Arson Shaft may be found midway between the entrance to the Stake Pot Series and Bob's Boss. A hole in the south wall is a window into the shaft which descends 17 metres and ascends 26 metres. A rope (replaced in May 2015) belayed to CNCC P-hangers with stainless steel maillons is ascended past a rebelay to a narrow exit a few metres above the floor of a blind pit. The rope continues up a further 5 metres to a short section of rift passage. Round the corner a final 10-metre pitch ascends to a traverse leading to a junction.
The way on is into the inlet passage entering from the left. A little small and grabby at first, it soon becomes more comfortable and starts to descend. It's impressively calcited, and must once have been a beautiful passage. After a few minutes an 11 m pitch is encountered, with inlets entering from passages at its base. This is also rigged with a fixed rope, which allows an escape if Aquarius Pot proves to be too damp. The way on is with the water through a rather gloomy phreatic passage which soon develops a vadose canyon at its base. Aquarius is met just beyond a couple of cascades. This pitch has only been P-bolted for a pull-through, and two P-bolts before the pitch head allows protection to be set up for the rigging of the shaft. A couple of 30 m ropes suffice. The pitch is not vertical and has a ledge near the bottom, so be prepared for the mud collected by your caving suit in the crawls to be washed off on the way down.
Below Aquarius a low passage leads to a cascade, below which is a hand and knees crawl in a shale bed. This starts to cuts down when it turns a corner and hits a joint, and becomes walking size. After forty metres or so, the water disappears down a narrow rift in the floor. The easiest way on is to climb back up into the roof bedding and traverse forward until a couple of bolts allow a descent of a 9 m pitch. The water is rejoined at the bottom, and five minutes of awkward going arrives at the Master Cave just upstream of the Stake Pot boulder pile.