I went through the tunnels with one of my friends for something to do during a hot day/short visit. The tunnels are fully air-conditioned and there are plenty of cafes and mini restaurants/takeaways in there. Free wifi in certain places too. At the very least it beats walking on the streets and melting during summer! Just note that the tunnels are only open on work days for the CBD (Monday to Friday excluding public holidays). Worth a visit though! Would like to see some more shopping maybe open up in the vacant areas.