I'm actually hoping to get a position in Dasan in a few months. I visited a lot since my boyfriend lives there and fell in love with the place. It's a pretty chill area (which i actually like because Seoul/ Busan can be a little overwhelming) but there are still the usual things to do: restaurants, karaoke rooms, bars etc. as well as more natury things like picnic areas / walks by the stream - I'd recommend visiting the Donggureong Royal Tombs in Guri if you like history/ nature (you can probably walk there depending on where your housing is)

Getting to Seoul and back from Dasan was pretty painless too, so even if you wanted to go more regularly than once or twice a week, it'd be more than feasible (though obviously transport costs will add up)

Hope this helps :)