They did it with mirrors. That's the theory anyway.
The other thing that causes this theory to falter it the ability of any mirror to deliver light down three hundred foot shafts and make multiple turns while maintaining reasonable luminosity.
Do not mistake this as that I believe they used electric light or something. It is just one of those interesting conundrums out there.
People are fantastically creative and clever when an objective must be attained; sometimes we just need to dig deeper.