Glenlyon Caves and Viator Hill Caves (collectively referred to as Texas Caves after a nearby town) are the only two major limestone cave areas in south-eastern Queensland. Unfortunately, they were drowned by Glenlyon Dam in the mid 1970s, in an act of sheer environmental vandalism.
To get there, you need to drive for a long time, especially if you are coming from Canberra! My suggested route would be to swing out to Cowra, then go through Molong, Wellington, Coonabarabran, Narrabri, Ashford (visit Ashford Caves while you’re there), and then around through Mingoola. Just after you cross the Dumaresq River, you need to do a sharp left turn onto Glenlyon Dam Road, and this road goes around to the dam wall. don’t drive all the way to the dam wall though, the turn-off to the Tourist Park on the right is in about 5km, with another right turn taking you down into the park. Camping is on yourt left as you drive in, the main office on your right (good source of ice-cream), and the caravans/cabins in front of you across the creek.
From Brisbane or Toowoomba, you have a range of options, but I would suggest sticking to the main roads- some of the unsealed back roads that are marked on the maps don’t go!
Once you’re at Glenlyon Dam, you then have to get to the caves, which are located part way up the dam- the top of Viator Hill is always above the water level and can be spotted in satellite imagery at -28.933798 S, 151.458021 E. Glenyon Caves is across the river from Viator Hill to the north-east. You have three options: you can hire a boat from Glenlyon Tourist Park (the rates are pretty reasonable for a group), you can bring your own boat (or kayaks), or you can walk around the edge of the dam. It’s probably 5km or so up the dam by boat, but significantly longer around the edge on foot, especially if the water level is high. Make sure you bring a hat and plenty of water, because the it is very hot and exposed on the limestone.
Glenlyon Dam is extremely popular with fisherfolk, as it is a well known Murray Cod fishery. Hence, the area has a very well set up Tourist Park, (http://glenlyondamtouristpark.com.au) with camping and accomodation options. The Tourist Park has a small store, but you’d be well advised to bring your own supplies. If you’re camping, watch out for ticks- the local kangaroos sport some absolute monsters!
There’s also a small museum about the dam and caves, which is worth a visit if you have time and it’s open.