We don’t go here often, but Wombeyan has some fantastic marble cave with excellent formation.
Head out of Canberra to Goulburn, and continue out of Goulburn to the north on the Taralga Road. After passing through Taralga, you soon come to the locale of Richlands, and there is a signposted turn to the right to Wombeyan Caves. Follow this until it plunges down a hill to the campground. Camping and cottages are both available; us stingy cavers almost exclusively camp.
You can also get to Wombeayn from the east, as there is a road coming in from Mittagong. This is dirt, very windy, narrow, has lots of wildlife, and can get in very poor condition. There is no reason to take this road from Canberra except for a scenic drive, and coming from Sydney, it takes just as long as driving via Goulburn. It is certainly not recommended for vehicles with low clearance, or for towing a caravan/trailer along. But with a 4WD it is quite a nice trip!
Wombeyan is extremely well set up, as it is a very popular tourist cave destination, second only to Jenolan in New South Wales, and on par with Yagby. There are hot showers, flush toilets, fireplaces, some cooking facilities (you’re better off bringing your own though), potable water, and a cafe/kiosk thingy. There are also close to a billion Eastern Grey Kangaroos, Satin Bowerbirds, and Wombats.