Where is Tobi's teleportation space location? While battling with Tobi, I have seen ninjas getting teleported to a place, which is kind of a dark room, having floor made up of blocks.

Is it a real place like a cave somewhere far? Or is it Tobi's subconscious mind?

Justification is required when considering a fighting scene between Tobi and Kakashi-Naruto.

When Kakashi is teleported into that place, Kakashi counter attacks with Kamui making Tobi bleed (cough blood). And Kakashi manages to return back to battle field.
It's explained in more detail in the manga. Anime viewers wouldn't know exactly what Tobi's power is.

That location is an alternate dimension, unique to him.


   Actually, since Tobi has the same eye as Kakashi, their dimension is shared. Tobi can freely insert and extract objects to/from his dimension. Kakashi can apparently insert things from a distance, and extract them directly from his eye.

 Kakshi's counter attack happened because Tobi used his Kamui to teleport a part of him (that was going to get hit in the 'real' world), to the alternate dimension. Kakshi was waiting in that alternate dimension and hit him from there (in the stomach, causing him to spew blood). Kakshi later returned to the real world with his own Kamui.