Cagliari is the capital of Sardinia.
Taxi service to Cagliari is provided by the following companies:
Cooperativa Radio Taxi “Quattro Mori”
Scalette Santo Sepolcro, 2 Cagliari Tel: 070 400101
Cooperativa Radio Taxi “Rossoblù”
Via Duomo, 19 Cagliari Tel: 070 6655
Bus servie to the city is provided in the daytime by ARST Azienda Regionale Trasporti (free toll 800 865042, info 070 4098327).
By public transportation
Cagliari Public Transportation CTM provides an fast and efficient service to get around in Cagliari city and suburbs.There are about 30 lines of buses and four new metro lines are in progress. At least the bus traffic is amazingly efficient and reliable to Italian standards. 
It is really difficult to get parking and drive in rush hour even if the road network has been recently improved.
The best thing you can do is walk through the old city and discover it. Almost everything you have to see in a quick visit of Cagliari can be joined by a pleasant little walk.
Wear comfortable shoes, though. The old town of Cagliari lies in a somewhat steep hill, so you will be walking uphill or downhill most of the time.
There are clean public toilets in the building on the Pontile Sanita ferry wharf, near the bus terminal.
The Cagliari bike station is in the centre of Cagliari, inside the parking area, at the train station. 
You must have a full relaxing day on the wonderful Poetto Beach. This 8 km beach will excite you and is perfectly equipped to satisfy every your wish. You can get here by buses PF, PQ, 3P, and 9P.
The beach is divided to the free parts and the beach clubs, the latter charging you with an entry fee but rent umbrellas, deck chairs, etc. for you. Prices are around €3/entry, about €12 for an umbrella, a deck chair and a sun bed. The club beaches clean the sand each night and provide you with showers and toilets.
Most of the shops are concentrated in a couple of areas: Via Roma and Largo Carlo Felice, the pedestrial roads Via Manno and Via Garibaldi, and the part of town around Via Alghero, Via Paoli and Via Dante. Lots of beautiful shop are concentrated in this areas which could remind you of Copenhagen's Strøget.
There are many of restaurants in the old town area, and you probably will not make a bad selection anyway since the food seems to be top class at least if you enjoy seafood. A dinner for two with little house wine.
There are a few places to enjoy lunch salads at the Piazza Yenne and wonderful Gelaterias if you don't want to eat too heavily during the day. These places double up as decent eateries by night.
The whole area around Cagliari gives host to a number of accommodation options including the world famous Forte village , and the stunning hotel Le Meridien Chia Laguna on the white sandy beaches of Chia.