And research, and more research. So much research that you face the real danger of falling down the rabbit hole and evading the writing that way.
People make good sources. If you contact experts, by email or what have you, they often love to talk about it. Beware, you can lose lots of hours that way.
Photographing buildings is a ticklish topic. You want business cards. One panelist was photographing a bridge after 9/11 and saw the cop watching her very, very, very closely. So she walked up to introduce herself and hand over a card. It helped, though you may be told to clear off, and they have the right to insist.
Sensory details are important. Don't just go by photos. You need to know how things smell and other telling details like that. If you can't go in person, ask. Things like how sandy the soil is in vinyard. What does a caribou smell like. etc. These telling details lend versilitude like nothing else.
Research has a wonderful way of turning up weird facts. And a panelist had put footnotes in her Regency to justify things like Windermere rather than Lake Windermere -- which, strictly speaking, is redundant because a mere is a lake.
Then, there's the point at which you must cut it off. You will never get it all right, and at some point, you have to escape the rabbit hole and write.