Biking in a big city

You can accomplish quite a bit on an indoor trainer but it can get a little boring. I will usually scout out the area around me to find some loops that are low traffic and free of too many stop lights or stop signs. It's better if they're at least 3 miles in length. I then try to ride the loop around a consistent time of the day so people learn to recognize me. Try your best not to be annoying to the cars around you and ride in a reasonably confident manner but not so much that you look arrogant. When you turn or change lane seriously exaggerate your movements to give the cars around you a sense of what you're about to do. If someone inadvertently cuts you off or is too close to you and only your feelings are hurt, try to brush it off and keep going like nothing happened. If someone honks or yells at you wave like you're their best friend. It's very confusing to them and they don't know how to respond.

It can be pretty dangerous out on the road but if you're careful you can at least minimize the dangers.

Basically, for weekday rides before/after work, the trainer. There just isn't any other solution that works for me and allows me to consistently get a quality workout. I don't even think about going outdoors for rides under two hours here--just not worth the risk and trouble, even if it was on the weekend. That's true even for pleasure rides. At three hours and up, I start to think about doing some/all of the workout outside. What that means here is an industrial park which is closed to outside vehicle traffic and has a fairly safe 4 mile-ish loop. I don't think I've done a training ride on the roads here in years. I do sometimes take my MTB with a group for fun rides out in the surrounding countryside.

Even in Oregon, I do my shorter, more intense stuff on the trainer (usually 90 minutes and under). For two hour-ish rides, sometimes a rural MUP about a 25-mile drive from my house. But I don't think that would be doable on a typical workday, if I worked in my hometown. It's my experience that urban MUP and "bike trails" tend to not be very safe for fast riding, or riding a tri bike in aero. Too many pedestrians, dogs on long leashes and off leash, kids entering the path at random from trailside parks, and, at least in my town, what we might politely call "impaired people"--people who aren't paying any attention to their surroundings because they are drunk, stoned, and/or plugged into personal electronics. Traffic and the stop and go nature of riding on urban streets make that a difficult way to get in a workout as well.

If one of the goals is to be social and meet some bikers, maybe find a used road bike (or rent or borrow one) and join some group rides? At least that would enable you to meet locals who could share some routes with you. If the goal is a quality workout, I'd stick to the trainer. It's just so much more convenient and efficient.

Don't know how far you are from Stone Mountain but they allow (at least did when I was there) bikes in for free. The road debris are brutal on the way in though and it's easy to get some flats. Other than that, I'd try a nearby park and do loops.