The Cotter Reserve is a large patch of gorgeous bushland surprisingly close to the city centre.
The wildlife is both a real treat and an absolutely genuine danger - this is a brown snake (the most likely snake to kill) wandering across the playground. Combined with the nearby water and the lack of fencing around the playground, it is definitely a high-supervision area. We also saw wombat holes, fish (both small and large), lizards, and plenty of cockatoos.
I liked the gentle blue and yellow colouring of the playground itself, which is one of the largest, best, and least populated in Canberra - even on weekends. It had a range of slides, wheelchair access onto part of the structure (although I imagine the tambark wouldn't be helpful), and several unusual features.
It would be a shame to go to The Cotter and not take kids for a paddle in the beautiful (although often silty) water. The playground section of the river isn't suitable for swimming (unlike nearby Casuarina Sands) but it has enough depth (and slipperiness) that a change of clothing is a must. Some of the submerged rocks are sharp, so "water shoes" are very useful.
Mobile phones have absolutely no reception in the area.
The playground is located after the Camping Ground and at least one other carpark. You can find it easily if you turn right just after the second bridge. It is very close to the dam, and some fantastic walking tracks with bite-size pieces of information about local history.