The
charts from o-charts are very good. If you are simply playing around a little, you can also try to use
https://map.openseamap.org/ and export those maps into
OpenCPN. Some are reasonably detailed to use, and some are too large scale for real plotting but at least give you the general info. OpenSeamap is free, I like using it to show someone a general idea of
ports and
anchorages and potential trips, but I can't always get a very detailed map in some areas (such as
Croatia, there are some maps that come in very well, and some that stay at large scale and not safe for plotting with.