The Mt Alexandra Reserve Circuit Trail appears to be a relaxing 2-3 hour stroll in the bush when viewed on the map. It remains true to this in real life; at least it does until you get halfway through, wherein it turns into a never-ending uphill march.
Lake Alexandra itself is worthy place for outdoor lounging-about. Arranged around the lake are at least ten picnic tables, some of them covered. The area also features a playground for the kiddies, a dodgy fountain in the centre of the lake, ducks, and some beautiful red leafed trees if you visit in the autumn or early winter. It is ten minutes from Mittagong Station, and the starting point for many of the walks.
Mittagong visitor centre sells a booklet for about $4 that details some of the walks in the area. However there is a map which is exactly the same as the one in the booklet online here. The circuit walk is the one beginning at Lake Alexandra in the bottom half of the map and taking a sharp turn back as it hits the Hume Highway.
The first part is all dappled sunlight, wide paths, and birdsong. It is clearly marked out except for the very first fork in the path (turn right). You'll know where you are because it follows the creek for about 30 minutes until you see the gargantuan pillars of the Hume Highway overpass just ahead. Following the path straight ahead here will lead you to much longer walks. If you'd like to do the circuit, follow the scraggly path that ascends sharply up the hill to your right just before the Hume Highway.
This is where the effort begins. The uphill will continue for quite longer than expected, especially if you are only a casual walker. The top, if you eventually get there, leads to the Katoomba lookout. It doesn't look much like Katoomba, but you can admire it anyway, as benches have been thoughtfully provided for you to do so. Another satisfaction is seeing the highway far below and realising just how far up you've come. The view stretches along the entire horizon.
On the way back you can do a short detour to the coke tunnel, once used by the area's coal industry. It adds an extra 300 metres or so, but there is also a large rock overhang just beyond the coke tunnel if you'd like a place to sit in the bush for just a bit longer. After some knee wobbling downhill, the walk returns to the lake.