This is very simplistic but it helps, I bought a couple of those little plastic caps that go on the end of bar stools and raise the back of the lapbook up on those. I also bought a little usb fan and sometimes blow that over it. I am not sure if that does any good though because the laptop has to generate the power to run the fan to cool it??? Macbooks are notorious for running hot!

Dip it in ice water.

Do you have it on a smooth, flat surface? If it is sitting on your lap or on top of your covers in bed it will get really hot.
If you are already on a flat surface, tilt up the back side with some kind of spacer (a book) to increase airflow. If it still overheats: turn down the display brightness, and don’t plug in other USB devices. If it still gets hot, your battery is shot and is not holding a charge. Replace it.

How do you know it is 70 degrees? Is that Fahrenheit or Celsius? If you are using one of those temperature monitoring utilities then those temperatures are frequently incorrect. Those sensors are designed to keep the computer from overheating, not to be perfect thermometers. The regular operating temperature of the processors are usually up around 150 – 170 degrees Fahrenheit. The computer will get hot, but that is normal. Unless it is actually shutting down from being too hot or you are having other issues like random crashes, then it isn’t really a problem for it to be warm.

My exboyfriend bought a fan-type thing that plugs into your USB that sits under your computer to cool it down. He has MacBook Pro with the aluminum (or whatever it is) casing, so it’s especially bad. I think he got it on Amazon and he’s pretty happy with it.