Fourmile Castle, a Second Life project which can be found at this SLURL.
I’ve had an avatar in Second Life since January 2007 after being introduced to the educational possibilities by a couple of guys from the Open University, and Fourmile Castle is my personal project as opposed to the “Warwick University Maths” island highlighted on other pages. It started off as an extension of a worksheet I used to use for NAGTY summer schools (Gifted 11-16 year old kids) when we visited the local Warwick Castle, and was designed to organically grow from a simple tower and battlements how a real castle might develop (with care taken to consider how main routes into the castle could be protected by defenders). The estate itself now straddles nearly all of the Fourmile sim along with large amounts of neighbouring Maceday and Cavanaugh, the current extent can be seen in the map below (the non-blurred parts):
The slideshow below (click on image to advance slides) shows how it has grown over time from Febuary 2007 to August 2011:
Of course, once you start a project like this it’s easy to get carried away, and in addition to a study of castle defences over time I’ve added secret rooms, a mine, and various rental properties around the sim which help pay for the monthly sim fees. There is also my popular 3D Maze (like a normal maze but on 3 levels with ramps between) and the main shop for my main business enterprise, “Ee’s SLideshow Viewer“. A selection of views of the estate is in the slideshow below: