Soldiers Pond is a beautiful swimming hole directly above Fort Amherst, St. John's. The swimming hole is across the water from Signal Hill and offers a beautiful view of it. It is also along the East Coast Trail and is very easy to find if you know where to look.
This is a great spot to swim as it is literally in St. John's. The parking lot is across the harbour from downtown St. John's, here is a link.
Once you park you will continue down the road and past a couple of houses until, to your right, you see a stream of water and signage for the trail. If you get to the lighthouse at Fort Amherst you have gone too far, although that is another cool spot which I will make a blog post for as well.
Once you get to the trail start heading up the mountain, although it is a fairly steep and tough climb, the view from the pond makes it worth it. You should probably wear sneakers or hiking boots, but I have seen it done in flip flops (not recommended). The trail is easy to follow, and once you reach the top it is impossible to miss the pond, which will be to your right. Here is a link for the pond.