The most impressive building in Västeräs is the large cathedral called Västeräs Domkyrka which basically just means cathedral. The construction of the cathedral was begun in the 12th century but most of the current cathedral date back to the 14th century. The cathedral is quite large and it is actually free to enter so if you are in town there really is no reason not to go in and have a look of the old church.
One of the interesting things of the church you actually spot right when you get inside the cathedral. At the entrance you see an old church door which is actually the last remaining original door from the old church. The original door has long since been replaced by a newer door but they have actually preserved the ancient wooden door.
Inside the church there is a large alter piece which looks good and the old coloured windows is a nice sight from to see with the light shining in through the coloured glass.