There are 2 everlasting portals/blackholes around the map. They never disappear, but ones you or someone else you can place around map, do disappear. The portals really only function, besides spitting out mass that you put in, is to teleport you. Putting 10 mass shots (or W's) into a portal will cause it to eject 20 mass shots back out around the portal. However, be careful going into the secret rooms A.K.A SRs with a lot of mass because you will start to decay pretty fast, and by a lot.
The easiest and free portal to get to is in the first secret spot. To get there, however, you have to go to the bottom left, and then there is a secret entrance in the bottom of the map, in either tiles E1 and E2, or D1 and D2. Once you are there, you can just go into the portal, and it will transport you to the top left corner of the map. Going into this portal will not take away any mass, and will not recombine you. If you are split up into multiple pieces, when you are teleported you will spawn in a straight, vertical line. However, the portal isn't the only thing in there. You can find an instant recombine, a 2x speed powerup, and a mass boost.
Portal number two is located in the second secret room, in the bottom right corner (E4 and E5 or D4 and D5). Going through the portal teleports you to the top right corner of the map, and sometimes a little further away from the top right. Really, this is the only secret room because the first secret room isn't really a secret. Now I'm not going to tell you how to get to the second SR, but I can tell you that is has something to do with the other SR. In the second SR, there isn't just the portal, like the first room. You can find: A recombine powerup and a 2x speed powerup (I havebeen told that they respawn every 1 to 2 minutes), and 3 mass boosts that spawn around the same time (don't know how often they respawn). The powerups are the reason why the second SR is a secret.
You can buy portals in the Shop, in General, for 39k coins. It will show up in your inventory, and then you can click and drag it from there to where ever you choose on the map. It will teleport you randomly to any where on the map. You can also buy portals and other items with real money.