The first stage of the exhibit consists of a few simple objects where fractals have been used just as textures. Not much more could be done with fractals in the early days of SL, not without using hundreds of prims for a single fractal. So the first fractals I've worked with inworld were no more than textures. 2D fractals mostly on the Mandelbrot Set and Julia Set which were like the big colourful ones you'll see on the walls underwater in the exhibit. The green sea floor is also one of this kind of fractals, edited with GIMP to remove the seams. There's also some small glowing plants, the red ones use the most common and known Mandelbrot fractal, the cycling ones use a "Fractal Flame" as texture as well as the vortex floor you land on when you teleport underwater.
For Julian, Mandelbrot and a few other fractals I've used Fractal Explorer.
Flame fractals were created using Apophysis.
Now, as I've mentioned, there was already a way to play with 3D fractals even in the early days. If you feel curious check the Second Life Geometry section Paul Bourke's site. There's lots of pictures there and even a few LSL scripts to generate fractals using prims.