I don't have a top ten, per se. Its a huge, diverse place so it really depends on what your style is, the sort of things that you like. I also don't know what time of year you're going so that also makes a difference. Personally, I'd spend a day or two around Muscat, maybe the day of your arrival and part of the next day. There's a lot to see and enjoy around town... you can easily spend a day checking out the city, getting your bearings.

After that, I'd consider going out to some of the great swimming places along the coast. If you like history go out to the forts and older archaeological sites. If you're feeling a more touristy vibe, you can take an afternoon or even multi-day dhow trip to somewhere. The landscape is breathtaking, and so in the right place/season you can do endless hikes ... even around Muscat you can do long walks that take you through water holes and waterfalls...I'd really recommend that. You can do these things as a day trip or over night.

You can also fly out to Salalah, which would easily fill up the rest of your trip with the city and the countryside surrounding it. This list from Rough Guide is actually pretty good: http://www.roughguides.com/destinati...hings-miss/#/0. This overview of the possibilities is also good: http://www.roughguides.com/destinati...n/where-to-go/.

I'd consider renting a car, unless you plan to spend the majority of your time in the city itself.