Easy. (as a glance at my watch)


As a pilot, night dead reckoning is similar to my response to your first scenario and I use it. Towns glow and if you can shoot two points, you know your exact position. If you know your average airspeed, and when you started, or last crossed a mapped landmark, you can tell where you are with one point, but two or three are always better.
Working with stars or the sun takes practice, a general astronomy knowledge, and a good clock, but that's how ships navigated prior to GPS for 250 years.
Google "Harrison Clocks" for some adventure. John Harrison won the "Longitude Prize" after many years of trying to convince the Royal board on which Issac Newton sat.
Also, Captain William Bligh (the Bounty) was/is considered one of the best navigators in history. It's amazing what he could do with a small boat in 1789.