I'm on a 90-day visa-free entry in Korea and my time is almost up?

This is the classic 'visa run,' and while people used to do it, it is risky and no longer a reliable strategy, so I would be cautious. Technically, if you leave Korea and re-enter you may be granted a fresh visa-free period, but there is no guarantee. Korean immigration officers have full discretion at the border and can see your travel history; if it looks like you are using back-to-back visa-free entries to effectively live in Korea rather than genuinely visiting, they can deny entry, grant a shorter stay, or pull you aside to question your funds, purpose, and ties. This has become more common as the system tightened, and a refusal can leave you stranded.

It also helps to remember that visa-free entry is meant for short visits, so repeatedly resetting it to live, work, or study here is outside what the status is for, and any unauthorized work on it is a serious problem. If you genuinely just want to keep traveling short-term and you have a real reason and the funds, a day trip to Japan and back might work, but treat it as uncertain rather than a guaranteed reset. If your real goal is to stay in Korea longer term, the proper path is to get the right visa for your situation, which usually means applying at a Korean embassy or consulate abroad, and that is far safer than border runs. Before booking anything, call the immigration hotline at 1345, which has English support, and ask directly about your nationality and situation, since the rules and the practical risk depend on both. And whatever you do, do not overstay, because that brings fines and a possible re-entry ban.