Pentax Forums, of course! I'll search old threads when planning a multi-day photo trip somewhere new, plan my general itinerary, then start a new thread to get more ideas.
I will usually browse
Google Maps when I plan to visit a new area. Flip between maps, satellite, terrain to see if anything catches my attention. Turn on street view to see if any pins have been dropped near interesting landscape spots away from a road. As I find potential spots with my Windows PC, I'll save flags so they show on my phone as I'm traveling.
Weather.gov for their Hourly Weather Forecast, with graphs that include not just the usual rain and temperature, but also cloud cover %, fog, aviation ceiling height, and visibility.
Wikipedia.org is a quick resource for researching new cities. Geography, arts, culture, architecture, and other places of interest.
Roadtrippers.com is a good tool for finding side trips between my current location and my next destination. You can filter on many different categories. Available as a website and phone app.
The Photographer's Ephemeris - Web App for checking sun/moon angles and times. For research purposes I prefer the website version, available for free, because of the larger display. I also have the inexpensive companion Android app,
The Photographers Ephemeris (TPE) on my phone. That plus a little trigonometry (for building height) is how I knew where to setup to get the moon behind the Empire State Building (photo below).
Sun Surveyor is another useful Android app. It uses the phone camera to overlay sun, moon, and milky way paths onto a live view. It's great for fine-tuning my setup spot when I'm on site.
Photo Pills can do something similar, but I never used it because when I compared features Photo Pills was only good for Apple, missing too many features for Android.