This is a picturesque, easy route along the Taff Trail. It’s essentially an out and back route but I’ve tried to vary it a bit. This route is very extendable, you can carry on the Taff trail all the way into Cardiff and then to the Bay if you wish. When I was a runner this was my regular long run, as you can get up to 20 miles. 
Distance: 3.5 miles (although can be as long as you want)
Strenuous: easy
Teilo wag factor: 2.5 (has river beaches, and places to paddle but route can be busy with bikes)

Starting at the school head down Iron Bridge Road. Go under the road bridge and turn left. Follow this path round until it joins the paved route and turn left, going under the motorway. The Taff Trail turns right after this, follow this down to the weir, with the river on your right. This is particularly scenic in autumn with the trees hanging over the river.

Radyr weir is a good point to stop and have a picnic, or go do down to the beach when the river is not too high. Continue on the path, although there is a smaller path through the trees along here also, with some access to the river, if you have a dog that wants to paddle (be careful when the river is full however as it becomes fast flowing).

Exploring the river

Pass the footbridge bridge that crosses in to Radyr, and there is a path to your right that goes along by the river (you can also just continue on the paved route if you’re cycling or running). We dipped into the river again before turning back, but you can continue on this path for much longer if you wish, going into Hailey Park, Bute Park and then down to the Bay (it’s about 10 miles from Tongwynlais to Cardiff Bay, which is a decent cycle route).

You can just return the way you came, but in order to add some variety, I went into Forest Farm, where there is a tree carving, and some picnic benches. This comes out on the road opposite the Forest Farm outdoor centre. Follow this road around to the allotments entrance, then turn right. This path leads to a bridge, just before you cross this there is a path on the left that goes alongside the brook.

Tree carving at Forest Farm

Follow this until it rejoins the main route by the weir. You can go back the way you came, but to alter it a bit, jink right just after the weir, and about two metres in there is a path on the left that runs parallel to the main route through some trees. If you have a dog this gives some time away from bikes. It comes out at the top of the trail, and you can then turn left and follow your route under the bridge back to Tongwynlais.