Nouadhibou is the first place of Mauritania you will see if you have travelled all the route through Morocco.
Nouadhibou is a place never constructed to fit the needs of tourists.
There is very little to see inside the city of more around 60,000 people, but the nature here is of splendid beauty.
Nouadhibou stretches along a peninsula running out from and parallel to the mainland in southern direction. Everything is more or less sand, shaped by the wind, meeting the sea in several bays without any vegetation destroying your impression of really being in Sahara.

Although accommodation is very difficult to find, eating is better here than anywhere else in Mauritania. There is one simple explanation to this : foreign fishing vessels exploiting the deep sea fishing outside the Mauritanian coast.
As these often need a harbour, as well are obliged to land and process a certain percentage of their catch, many foreigners enter the streets. They want a decent meal, but sleep on their vessels, of course.

Daily air connections to Nouakchott, but you can also get to Las Palmas on the Canary Islands, Spain. You can travel with one of the trucks or Land Rovers that go overland to Nouakchott (30-50 hours), and the price is normally US$20 to US$30, but prices are not fixed.
Pay on arrival, and charge the drivers if you help with repairs en route. Faster connections to the south is with the train to Choum (about 250 km south of Zouerate), and use overland transport from there. This is far cheaper as well.
But for travellers with time, the direct connections south is a fantastic experience. Going north into Morocco, you cannot rely on any form of public transportation, but check around with travellers going this way (which happens to be quite unlikely due to the strict policies of Mauritanian border police).