Quite near Santander there are some interesting places to visit. Some of them are perfect for a free afternoon, others will take you more time and they are perfect for one day.
ETNOGRAFIC MUSEUM OF MURIEDAS- A quite interesting museum about the traditions in Cantabria in an old and traditional house. The guide will kindly explain but in Spanish. The buses are the A1 or A4 next to the Santander bus station. Ask to the driver to tell you where to go down and you should walk a bit.
VIRGEN DEL MAR- It´s a beautiful small island with a church and a small beach. That´s fantastic for one afternoon or if you prefer you can spend one beach day there ( there is a coffee shop but take better the food with you) . The coast line is quite impressive. Near there is the Santander cemetery with old graves. The city buses 2 and 17-2 stop at Corbán and from there you should walk a while, so the best option is the city bus 17-1 that stops at the cemetery and it is quite near to the beach.
NATURAL PARK OF CABARCENO- It´s a saffari experience in an old open sky mine. The best option is a car but if you don´t have you can go by bus and visit the area on foot or using some public transport there ( you will get informed at the ticket box). A lot animals in different environments and you will need a day, better to take everything you will need there and be ready to walk a lot. There are some regular buses to Liérganes or Sarón that will stop you quite near the park entrance but you will need to walk, ask in the Santander bus station for more information.
SOMO- From the old wharf in the city centre you can take a boat to this small town just in front of Santander. In the summer the boat company organizes some tours around the bay and you should check them. Santander´s bay is very beautiful so you "must" take at least one boat to enjoy it. Somo has a big beach where you can walk and some restaurants and bars, it´s good option for one free afternoon and it´s perfect for surf lovers. Another company that offers tours around the bay is Santander Bahia Tours.