From Selva de mar metro stop to Casa Batllo
The Casa Batllo, one of Antoni Gaudi's most spectacular monuments, is located on the Passeig de Gracia, at the foot of the metro station of the same name. To get to Casa Batllo, from Selva de mar metro station, simply take the L4 line to Passeig de Gracia station, you will reach at the foot of the monument.

Get to the Ramblas from Selva de mar metro station
To get to the Ramblas (the Rambla), by metro, from Selva de mar metro station, for example, you can take the yellow line (line L4) from the Selva de mar stop to Urquinaona and then change to the L1 line to get off at Catalunya. Note that the distance between Urquinaona station and Plaça Catalunya is easily covered on foot.
If you have a preference between the beginning, the middle or the end of the Ramblas, follow the L4 line from Selva de mar to Passeig de Gracia to continue your journey with the L3 line and get off at either Drassanes (Port side), Liceu (centre of the Ramblas) or Catalunya station.
In additional options, if you like to enjoy the city on foot, you can take the Selva de mar metro to Barceloneta and walk along the port to reach the Ramblas at the foot of the Christopher Columbus monument, or get off at the Jaume 1 stop and walk through the Gothic Quarter to the Ramblas.