Sir James sought out an underground military headquarters from which he could command troops and maintain an eye on logistics but also be out of sight when needed. In the end he commissioned a pair of underground headquarters, neither of which was really completed before his death.
This particular structure was not only incomplete, but Sir James never used it as its designer intended, instead using it as a decoy base. Construction was never completed and the front entrance to the structure (at the lower middle of the page) was collapsed to prevent it falling into enemy hands.
To enter the structure now, one has to come in through the ceiling of a chamber that was undermined during construction and subsequently collapsed (drawn as the hole in the upper-right quadrant of the map). The hole is a fairly recent entryway, and little of the underlying structure has been looted or explored.
The structure was evidently meant to be significantly larger when completed, but the vagaries of war and the the role it got pushed into as a decoy kept it from being properly expanded before it was buried.
This map is made available to you under a free license for personal or commercial use thanks to the awesome supporters of my Patreon Campaign. Over 300 awesome patrons have come together to fund the site and these maps, making them free for your use.
Because of the incredible generosity of my patrons, I’m able to make this map free for commercial use also. Each month while funding is over the $300 mark, each map that achieves the $300+ funding level will be released under this free commercial license. You can use, reuse, remix and/or modify the maps that are being published under the commercial license on a royalty-free basis as long as they include attribution (“Cartography by Dyson Logos” or “Maps by Dyson Logos”). For those that want/need a Creative Commons license, it would look something like this:
Cartography by Dyson Logos is licensed
under a Creative Commons Attribution 4.0 International License.
(And of course, I would love to see what you use it in!)