According to Baidu map, you can take subway line 3 from Confucius Temple to Xuanwu Lake, which is 7.9 kilometers apart and takes 34 minutes by subway. The specific route is as follows:

1. Walk 730 meters from Confucius Temple to Confucius Temple Station.

2. Take Metro Line 3 from Confucius Temple Station and arrive at Xinzhuang Station of Nanjing Forestry University after 5 stops.

3. Walk 500 meters southwest from Nanjing Forestry University-Xinzhuang Station to Xuanwu Lake.