Tamsui is a coastal town located at the mouth of the river of the same name. Taipei citizens love to go there for walks on the weekends. That's why both, the town and the subway are crowded those days. If you have the opportunity, it is better to go during the week, since you will enjoy the ride more.
The subway leaves you in the very center of town, where the Old Street and the walk along the river begin. Leaving the station, if you walk in front you have a YouBike station. And if you walk a bit towards the river, you will see that there is a bike rental stand, which has bikes with baby and child seats, and children's bikes as well. If you arrive early or it is a weekday without many people, it is a plan to rent the bikes and do the ride to the mouth of the river (Fisherman's Wharf) . But if you see that there are already too many people on the ride, better walk, because it is a real hell to carry bikes among the crowd. From the station to the mouth of the river (Lover's Bridge) it is about 5km (approx 30min). It is not worth doing walking, but if there are not many people and you have bikes, then it is a good plan.
In case you decide to walk, we recommend doing it to Santo Domingo Fort, which is about 2.2km (approx 20min on foot). The fort is interesting and is a good way to learn a little about the history of Taiwan and its Spanish colonial past. Children are often entertained. Admission is NTD 80, and it also serves to see the Tamsui Customs Officer's Residence (Little White House) and the Hobe Fort. But the truth is that the first one is not worth much and the second is a bit far. You will know that you have arrived at Fort Santo Domingo because on the river side bike path you will meet the Tamsui Customs Wharf, which is also worth browsing (free entrance).
