As cycling is my main way of getting around I hardly make use of public transport. When I do and it’s the subway, or metro as we call them here, and I need to go to the south part of town, I always make sure to stand on the side for a look over the harbours once the train gets out of the tunnel if you come from the centre.
The first stop after the tunnel is the Rijnhaven and from this stop you have a nice view over this body of water towards the Kop van Zuid area with the floating ‘forest’, the Floating Pavilion, the newest buildings Boston & Seattle on the right of the New Orleans building and to the left Katendrecht (De Kaap).
I suggest to get yourself a (borrowed) OV chipcard (public transport card) as you need this to enter any metro station. Check in with the card and take the line D or E towards De Akkers or Slinge and get out at Rijnhaven. Or cycle to Rijnhaven and take the elevator up from the street towards the platform where you would need that chipcard too for getting in and out!
Enjoy the view over the Rijnhaven (Rhineharbour) and I suggest visiting from 11am when the sun shines towards that part. And check the painted pillars from June on.
If you need to process that nice view with a drink, head down again to that lovely place Sharp Sharp just in front of said station.