In Stockholm there's a current ongoing expansion of the metro system, the blue line is being expanded towards Nacka to the east and to Bakarby on the northwest while connecting to the south on an expansion. A new line (yellow) is under construction, the green line is being expanded.

In total there are 18 new stations, digging under bodies of water (and quite deep through a lot of the blue line), total cost: around 5B€.