Staying in Jerez provies the oppurtunity to see more of Andalucia via the excellent bus and rail network. Being close to Seville and Cadiz, we chose a day trip to the latter.
A return rail ticket to Cadiz cost the ridiculously low figure of 3.95 Euros. The train station in Jerez is next to the bus station so you have the choice of mode of transport. Be aware that virtually all rail and bus staff DO NOT speak English so an understanding of basic Spanish is useful. The trains are clean, on time and guarded by a security guard which was a shock to start with but actually gave an extra sense of security (not that we ever felt unsafe). The journey to Cadiz is about 1 hour.
Cadiz is an old historic part of Spain that sits on a small dog leg of land. After arriving at the only train station (near the port), turn right and head for the city centre. Cadiz gives the feeling of a laid back, relaxed (and safe) town. It is very compact and you can easily walk around to see the many sites. Alternatively you can take a open top bus tour which if you are only visiting for one day will give you a wonderful insight into the city, it's history and people.
The old part of Cadiz is a paradise of 18th-century architecture, which leaves the visitor with the impression of Cadiz's previous grandeur, alleyways and narrow streets, numerous plazas and cafe/tapas bars. Walking around this part, you are taken back hundreds of years as things have changed very little. Again, although normal precautions are advised, the whole town has a very safe feel.
There are two clean beaches on the waterfront, which get very crowded during the peak summer.
A good place to start is the Cadiz Museum in the Plaza De Mina. The entry is free to EU citizens and has three floors of Greco/Romano/Phoenician artefacts, renaiisance and contempory paintings. Unfortunately all the descriptions are in Spanish, but in no way did this detract from the visit.
It is difficult to see all Cadiz and get under its skin in 1 day, but you can get a flavour that will leave you wanting more.