are.na-rail by larsilikum

Are.na rail
an are.na premium or supporter account is necessary for most of the functionality.
are.na rail is a webextension that lets you explore website link blocks of are.na channels directly in the browser.

starting from a random site
When browsing the web you can search for the current site you're on and find channels that contain this page. Then this extension lets you automatically commute from block to block or station to station starting from where you were. (The extension only displays channels with 500 blocks or less because of technical issues.)
starting from are.na
The other way you can start a subway ride is by starting directly from a channel on are.na. Just click the get lines button and you should be able to start the ride from this channel. This also enables to travel along channels with more than 500 blocks.

customizing the experience
The extension popup gives some options you can configure, like the time that the subway is staying at a station or the time that it takes to commute from on site to another, which is only available when using fun mode, which adds a subway animation for immersion.