To progress throughout the game, one of the most common resources you will use is Whetstones. Whetstones are used in many ways, so it’s always advised to keep a few around in case of need.
To obtain Whetstones, we would advise you to visit the Bandit Stronghold. This location might be a bit tricky if you dont want any PvE interactions, but you could play it in stealth mode if you are careful enough. The Bandit Encampment is also a nice location to farm for your needs, yet again, stealth might be preferred if you dont like PvE interactions for the time being.
These whetstones can also be found in loot stashes and barrels or other things that you can wack to destroy. In my personal opinion, I always grind down the whole POI, as it always can contain some nice loot. On some occasions, you could already even obtain glass.