Joshua Penny
By all accounts Joshua Penny was a free spirit who did not agree with the notion of subjecting himself to authority of any sort. He was born in New York State in 1776 "to a large and impoverished family. At age 14 his father got rid of him by apprenticing him to a local doctor. Penny did the blood letter's dirty work for just one year and then decided he was not cut out, as it were, for the medical profession and joyfully went off to be a sailor."1
His travels led him to Ireland and England where he dodged various attempts of being impressed into service by the Royal Navy, and in the process developed a healthy dislike for said navy. To escape their advances he joined a slave ship plying its trade between West Africa and Jamaica ("the irony of shipping in a slaver in order to escape from oppression seems to have eluded him")1
In the meantime Britain had developed aspersions for the Cape of Good Hope and as soon as Penny and his fellow seamen unloaded their cargo of 382 wretched West Africans in Jamaica (11 of whom, as Penny points out, had been impregnated by the captain and thus increased in value), they were raided by a press gang, and thus Penny ended up on a Royal Navy ship in Cape Town. (This reminds me of the tale of the two fleas and the Harley, but I will leave that for another day)
Several adventures later (which included desertions and a stint in the hinterland) he ended up on the HMS Sceptre (64 guns), which spent several months in Table Bay and gave him enough time to concoct a plan. He somehow convinced his superiors that he was sick and on their way to the hospital they stopped off at a tavern where he made his warders rather drunk. On the pretext of going to the toilet he escaped via the back door, and this is where this cave comes into the story.
Penny disappeared onto the slopes of Table Mountain. He rapidly adapted to his new way of life. For meat he preyed on dassies and small buck (plentiful in those days) and for greens he gathered roots and nuts. Drawing from his experiences of his Koue Bokkeveld expedition, he brewed honey-beer in the Hottentot and Bushman fashion. He made clothes from animal skins using a bone needle and antelope sinews. Time passed. Whenever it was full moon he cut a notch in a root he wore around his neck on a cord. After 12 notches on the root Penny ventured his way down to the harbour only to discover that the Sceptre had sunk with all hands on deck just two months after his escape.
Penny made his way back to America where he wrote of his adventures in the Cape. According to (1) a copy is available in the Public Library's Africana reference room.

In the 1958 MCSA journal is an article by WH Crump which relates this story and the location of the cave. The MCSA museum contains display cabinets of items retrieved from the cave by Crump and Inglis. The ossuary in Somerset Road contains the remains of the nearly 300 unlucky crew and marines who drowned when the Sceptre sunk in the most terrible of storms in Table Bay in 1799.
Mike Scott, well known in Cape Town hiking and mountaineering circles, wrote another article in the MCSA journal in which he describes various attempts in finding the cave. We were fortunate to be shown the cave by Charles Morrison who first found it again in 2005. Many thanks to Phil Wright (capeccr) who knew Charles and organized the expedition led by him.

Photo2 showing various routes tried by Mike Scott (blue), and the route we recommend (red), with the G-F-C traverse above.
The route is somewhat obscure and involves a lot of off-path route-finding. It is not any more difficult than any of the other famous scrambles on the mountain (Left_Face B, Grotto-Fountain-Cairn traverse, Kloof Corner, Spring Buttress) but my concern is that the route is not obvious, so I would recommend being accompanied by someone who has done it before. I have visions of geocachers falling off the mountain while staring at their gadgets. Reception is shaky and the terrain steep, so look up and around to look what you are doing.
There would be several different approaches to the cave, but I would recommend the one shown to us by Charles Morisson, as it is the most diverse and interesting and incorporates different routes to those familiar to regular hikers. After a bit of a slog to get to the rock band, Cairn ravine offers several nice scrambles, and the breakfast stop as you exit the ravine is stunning as you have a grand view of Kloof corner and the Cableway above. The traverse to the cave is along a steep grassy slope with no path. I recommend good boots with a hard sole and good ankle support. Long pants are also recommended. After the cave we climbed another steep slope on the right and then traversed a ledge below the well-known Grotto-Fountain-Cairn traverse into Grotto ravine. From there it was another vague bundu bash to Blinkwater ravine.
There could be various alternatives:
1. Following the route described above, but on reaching Grotto ravine head straight up past Grotto-Fountain-Cairn traverse and up North Gully to the cable station
2. Approach on the lower traverse via Grotto ravine and descend the steep grassy slope to the cave. Descending steep slopes or scrambles is more tricky than ascending. A long rope might be useful
3. Approach from Grotto-Fountain-Cairn traverse. This would require abseiling and ropework that is out of my league.
REFERENCES:
1. Curious Incidents and Hairbreadth Escapes (Chapter 2) - from "Poor Man's Bioscope" by Willem Steenkamp
2. MCSA Journal article by Mike Scott 2005+
3. Garmin gdb file of the 2013 track, the 2011 track and an earlier Grotto-Fountain-Cairn Traverse. GPS reception was shaky at times. The shakiness has been left unedited so that the extent thereof can be seen.

The famous Myburghian Leap near our breakfast spot as we traverse out of Cairn Ravine. Photographic evidence that great minds are packaged in small parcels. The nodule between the arms of our model represents the brain of FTR, which is driving the Western Cape geocachers to frustration with his puzzles. Henzz pointed out that FTR is poking his right hand into the eye of a baby-face and that he is jumping on the head of a baboon face.

First view of the cave from "Cave view" waypoint

Our model posing in the cave

View from cave. No wonder nobody could see it from outside.

Our model pointing to the cache site. He might well have diamonds on the buckles of his shoes.
Our time schedule:
1. Meant to start at 0500 but delayed to 0530 as dogs ate my sarmies and I had to prepare another consignment.
2. Pipe track below Cairn Ravine 0600
3. Rock band 0700
4. Breakfast 0830
5. Cave 0915
6. Blinkwater 1045
7. Back on pipe track 1200

View of the overhang where you exit Cairn Ravine. I believe it should be quite possible to get to this point via the "poort" on Kloof Corner ridge and descending Cairn Ravine. The trick would be to find this spot. GPS reception is shaky. There are 3 exciting scrambles up Cairn ravine - the first involves hugging a tree trunk, the second requires an ascent on the far right of a clifflet and the 3rd requires a gecko-like scramble up a sloping rock. The exit is only a short distance (100m or so) beyond this 3rd scramble.

Our models showing the way out of Cairn ravine.

The exit from Penny's cave, showing the traverse below G-F-C and the bundu-bash to Blinkwater (there are hints of a trail in places, but it comes and goes - further investigation is required)

Not the best photostitch, and the sun was in our eyes, but it shows the approximate routes of the Grotto-Fountain-Cairn traverse, Kloof Corner Ridge and the route we took for Penny's Cave.
Enjoy