The first project I did was to refinish the original hardwood I found under some grungy old carpeting in a guest room. The carpet was easy to remove but refinishing the floors took a lot of time.
I chose to chemically strip the floors since I was worried I wouldn't have enough thickness on the old tongue and groove planks to sand the carpet glue and prior finishes off. Chemically stripping was very effective but required a lot of prep work and time. If I were to do this project again, I would cut into a small section of a plank to gauge the thickness. Then I would have known there was plenty of thickness above the tongue that could still be sanded to prep for refinishing. It's important to get the old finishes off unless you know what they are, since they can prevent you from being able to seal the floor properly if you choose a finish material that doesn't match the original.
In between the planks, prior owners had filled the gaps with wood putty. Over time, the planks swell and contract seasonally so the putty works itself loose. I removed all of the putty which involved a lot of effort. I still wanted the gaps to be more filled in, since most modern floors don't have such big spacing between each plank. I chose to use a twine method which allows the boards to still move but prevents things from falling in the gaps. This was pretty easy to do, just roll twine till it's the right thickness and tuck it snugly into each gap on top of the tongue.
For sealing, I used three coats of Tung nut oil from the Real Milk Paint company. When I researched this project I found that several brands have mixers that make it less effective. Pure Tung oil can actually bind with the wood and strengthen it, perfect for much older floors. I used this oil to finish a plain pine Ikea bed frame too, it's a very warm and pretty finish. It does have a strong nutty smell at first, but that went away in a week or two. I used old clean socks over my gloved hands to rub the oil over the wood. This part of the project was very quick to apply but needed to dry for a while between coats. The Tung oil helped seal the twine fibers as well and gave a warmer color to the natural fibers.
Twine and Tung oil used to be used for finishing ships, so this is a nice long term way to seal old floors. I'll likely reapply a coat of Tung oil after 10 years, sooner if there are scratches that need to be fixed. I like it better than poly since I can use it for quick touch ups without redoing the whole floor. All in all, this project let me use materials from the right time period to refinish the floors but it is not the easiest way to go about things. If it were a bigger space I probably would have thought about using more modern techniques.