I have a "BahnCard 100" [1], the German national public transit flatrate. My employer pays for it in lieu of a company car. I only have to pay income taxes on it, which comes out to about 170€ (200$) a month. For that price, I can use all trains across Germany as often as I want and also get free local transit (busses, subway etc.) in 120 cities, including the one where I live.
2020 is my first year with a BC100, so due to Corona I couldn't use it that much yet, but it's kind of mind-blowing to go to a train station and just be able to hop on any train [2] whenever I feel like it, no questions asked. When Corona has blown over, I will definitely make a habit of just exploring Germany every other weekend.
[1] https://www.bahn.com/en/view/offers/bahncard/bahncard_100-co...
[2] There are some rare exceptions, e.g. night trains require a reservation.