Tachog Lhakhang sits on a hillside above the Paro Chhu about twenty kilometres east of Paro, on the road to Thimphu. The temple was founded in the 14th century by the bridge-builder saint Thangtong Gyalpo, and the iron chain bridge across the river below the temple is one of his original surviving works — the chain links date from the 15th century. The modern wooden footboards were added later; you walk across the same iron that Thangtong Gyalpo forged.
A small visit takes about an hour: a short climb up to the temple, a look at the wall paintings inside (the caretaker will usually open it on request), and the walk across the iron bridge to a small chorten on the far bank. Easy to combine with a transit between Paro and Thimphu, since the temple is literally on the route. No admission fee.