Originally the Twin 60s tunnel was a tributary creek leading into a much larger stream. In 1964, water flowing along this creek was diverted into two large concrete pipes and buried to accommodate the large industrial site that now sits above.
You can take either pipe. Each of its several sections are separated by large junction rooms. 750 meters before the exit of this 3 kilometer long tunnel it opens up into a single, standable segment, of which awesome street art enhances the normally bland concrete walls.