Ask them point blank. What's the culture like here? If I fail, admit it and fix it is there repercussions? How do you guys help newbee people come up to speed? What would my first week be like? Are there any company outings? Is it looked upon bad if I don't go cause I am busy? Are there any normal weekly events that happen? Is it frowned upon to write code outside of work for myself or open source? etc.<p>Visually: What's the environment look like? Do you see anybody laughing and having a good time, or is everyone's head down into their desk and not looking up? Are the machines old? Are the work environments nice (even if dated) etc. Look at how many layers of management there are.<p>BTW -- any awkward pauses on the questions or doubts on the visual and you already have an answer.
Ask them about their vacation policy, and specifically ask your interviewer when was the last time they took a vacation 1 week or longer.<p>Ask if they're remote friendly.<p>Ask what their sick policy is.<p>Ask what their company does to make the world a better place. It's fine if they don't have an answer, some entities exist just to make money without any other "mission", it's just good to know.
As you may have puzzled out from other responses here, that's a very personal question. You need to figure out the cultural details that mean something to you, then ask the questions that reveal them.<p>For some people that's vacation, for others it's safety nets, and for others it's engineering processes. Only you know what matters to yourself.