Indoors, between family and friends in a close setting where people are most likely not wearing masks is how the virus more easily transmits. It is not exclusive to indoors though.
I live in what was a hot spot in March, April and May due to our proximity to NYC. I can tell you for sure that some of the people I knew who got it contracted it at an outdoor BBQ. They did not follow distancing or mask protocol (back then, masks were not mandatory, as we were part of the first wave in the country and information was just coming out on how to protect yourself). They also had the mentality that "I'm young, it won't affect me". This was primarily a young age group of 20 somethings. When the first one got it and wound up in the ER on oxygen you wouldn't believe the fights and blame they all threw at each other. This is my dd's friend group and thankfully she had enough sense to recognize the potential of possible spread in a large group of people and she stayed home.
I'm seeing lots of outdoor things canceled up here because of the potential of spread; festivals, baseball, fairs, concerts, etc. We do not want to go backward when it took so long to slow the spread. JMO, from what I've seen and personally experienced with how it spread to people we know it's naive to believe that any large gathering of people in close proximity to each other won't/can't spread it, whether indoors or outdoors. My personal opinion is that you probably won't get it in just passing someone, but standing or sitting stationary near someone for a length of time past a few minutes increases your chances of getting it.
Again, JMO but I don't think anyone should be doing unnecessary travel right now. And I'm not basing my opinion on news stories, defending my rights, perceived hoaxes or threats. I'm basing in on having gone through the initial wave of infection living in a hot spot, knowing lots of people who have had it and some who have died and for me, it's just not worth it. Aside from that, our state has a mandatory 14 quarantine now if we travel and return from 16 states that are having a rise in cases.... so we won't be going anywhere for a while anyway. I'm actually glad they imposed that.