Hi, we are currently based in Northern Sardinia, and have had a couple of holidays around the area, and planning to be there in May, July and September, as last year.
We have anchored both inside the National Park, and also outside. Have found that the Navily app, free to download, is great for anchorages.
We did anchor one night in Cala Lunga on Isolla Razzoli, very peaceful with a lunar landscape. There is a
mooring buoy you can pick up, if you have a permit, holding
tanks, and a local boat! There were three of us in there, non local, non with permit, which I tried to buy online whilst we were there, but didn't manage, as kept kicking out when I got so far. We were not bothered by the authorities, probably because it is in the outer islands of the archipelago, not around Maddalena itself.
There are a lot of anchorages on Sardinia mainland outside of National Park, with no restrictions, all shown on Navily, with feedback from genuine users, me being one. Also we called into Madallena town harbour in September, which was really nice, lots of charector and plenty of restaurants. We have a 12m yacht, and from memory cost about 35 euro for night. We thought it well worth it, and will visit again this summer.
Outside of this, a trip into Bonifaccio on
Corsica is also well worth it, if more expensive. Cost us about 70 euro in July, and 40 euro in September, but again we will definitely be going back this summer.
Whatever you do, am sure you will have a great time, just remember that the winds through the straights can be very strong, and sea conditions quite lumpy.
Happy sailing