If you take the MRT all the way to Nanshijiao and then venture further south under the freeway to the edge of Zhonghe you will arrive at the start of the Hongludi hiking trail (烘爐地步道). Along the trail there are a number of interesting temples and stunning views across Taipei.
The first temple on the trail was the Guanyin Temple (觀音寺). It is not a small temple, but it is overshadowed by the larger temples above it. The next temple along the way was the Jingnan Temple (竟南宮). It is a huge sprawling complex with lots of colorful dragons on its roof.
At the top of the hill is the Nanshan Fude Temple (南山福德宮). It enjoys a commanding position on the top of the hill and was bustling with people praying and making offerings when I visited. The large statue of the Earth God (土地公) below the temple is a landmark visible from many places nearby.
There are great views across Taipei from all of the temples but the views improve as you get higher up. Behind the Fude Temple there is a hiking trail that continues along the ridge. The trail can be followed to Yuantong Chan Temple, also in Zhonghe, on the other side of the valley. It is also possible to hike to Tucheng but this trail is not clearly marked. I might try and follow it all the way next time.