My summer hobbies are all outside things. I like running and this is quality training time to get outside, get a tan, get attractive and go win some 5k races in the fall.

I also have a house and a yard so my hobbies have to revolve around mulching, planting, weeding, mowing the lawn, edging the lawn, trimming trees, and maintaining the yard. I like to look out there when it's all done, and go drink a beer with my wife while we swing on our hammock in the shade.

I also swim outside at the local pool. And I run with my 2.5 year old around the block to train her to exercise. She thinks it is fun and she's turning into a talented runner. We also play catch, soccer, and other outdoor games.

Lastly, I love night time during the summer. Our neighborhood has six houses, next to each other, that are occupied by guys about my age. We drink beer on the sidewalk and look at our attractive wives and sometimes we drag out the grills and cook food. It's very social.

Since I live in a higher latitude (43 degrees), I usually take advantage of summer to get the vitamin D I can not get otherwise. Be it by moving the lawn, taking off my shirt when I walk around or simply sun bathing, I take every opportunity I get

In all honesty, what I usually do in the summer is this.
Lay in my bed, watch DBZ, eat watch DBZ and then sleep. At least this summer. I hate heat and I don't feel warm when I'm just being calm

Otherwise i just speedrun/TAS games because i like that

Honestly, I sit in bed all day, sometimes go swimming at the pool near my house, watch a tv show (this year's TV show was everybody hates chris) and text some friends.

I don't really get out much, so I normally just stay indoors other than playing sports outside or swimming. It may not be the most fun ever but whatever, its acceptable. 

TheJmsGamer : I like speedrunning too but I haven't done any TAS'ing. I'd much rather see how good I can get with my natural skill in one go, sometimes I even do things near-perfectly when I'm really concentrated on my game I think I'll only be speedrunning during the summer because during the school year I don't have as much time to play video games.

Barathemos : My neighbor has a pool so I also go to a pool near my house once in a while. I live a few blocks away from a YMCA so I go swimming there too, mostly during the summer. I swam there tonight with my family (that was the last plan they had for me today after all that I mentioned earlier ).

Mostly I just stay inside and surf the web. More and more, however, I've been getting outside and into the sun. Usually to play some ball with my friends or just to take a walk.

I also like to work out, especially since now I have far more time to do all the training I want to.

IStillSeeTheX : Cool, I've been getting outside more too. It's hot and humid almost all the time outside during the summer here. But since I'm used to it I can still be out there for a long period of time, enjoy it, and not go inside until I'm tired of running around. XD

One of my favorite things to do during summer is stay inside in an air conditioned room. xD

I hate the heat and try to avoid going outside as much as possible until fall. 

I get outside as much as humanly possible. I live in Michigan in the United States and we get snow and it's cold for 4-5 out of 12 months a year. It is a struggle to stay cooped up inside when it's 10 degrees or the snow is falling and I want to be out longer than 20 minutes.

The summer? I go to the park with my kids and we run around for an hour or two.

I go to the beach with my kids and my wife and we play in the water, we go to the playground, we dig in the sand and generally have fun in the sunlight. We'll get a kite or two up and leave them pegged in the dirt or the sand so they can stay in the air without someone having to hold them. That's usually a nice touch.

We'll also take vacations out to new parts of the state or country and see things and visit places we haven't been to before. I enjoy this and I like trying new and different food I've never had before.

I also play sports, like baseball and soccer. I sit out on my patio or in the hammock with my wife and we drink beer or wine and watch the stars, talk, or look at the little fire we start up. We might even make s'mores if we were so inclined.

The outdoors offer so many things to do. I wait around in March for the weather to turn so I can get outside as quick as possible. Outside is awesome and I find being in the house is so boring.