So you've landed on some post on reddit.com, read it and now wondering how to view the whole subreddit.
Maybe click on its name in the top left corner? Nope, it opens a global site-wide menu which includes incomprehensible things like "Coins".
Maybe click on the reddit logo? Nope.
One of those icons in the top right corner? Nope.
No, no, no. To get from a subreddit post to the subreddit you have to click "Close".