The Département du Gard includes three main natural regions: the coastal plain and swamps of the lower Rhône, to the South; the "garrigues" (mediterranean shrubland, here used as a geographic name) in the center; the Cévennes mountains to the North.
The plains and the Lower Rhône area are rich in historical towns and sites, including lots of Roman remains (such as the Pont du Gard aqueduct, or the amphitheater in Nimes). The Cévennes are medium altitude mountains (1565 m at Mont Aigoual), but offer sensational landscapes as their southern slopes is actually quite steep. The garrigues, in the middle, are limestone plateaux with caves and gorges, some wineyards and many small villages with white houses and shady, winding streets.
The Gard forms the Eastern portion of the Languedoc (the historical province rather than the administrative unit), and despite proximity and similarities does not belong to Provence (located on the Eastern side of the Rhône). The locals will appreciate it if you do not add to the confusion.
Since the 16th Century, the Eastern Languedoc (present day Gard and Eastern half of Hérault) has been a Potestant stronghold, and was greatly affected by wars of religion in the 16th to early 18th century. Interested visitors can discover this history in the Musée du Désert in Mialet, near Anduze.
Climate is generally pleasant, with hot and dry summers, mild winters, warm springs and autumn. The weather is dry and sunny most of the time -- with 3/4 of the rainfall concentrated in Autumn (late September to October), typically during a handful of cataclysmic thunderstorms ("épisodes Cévenols") lasting a day or two, but accumulating up to a quarter of the yearly rainfall in a day. The region is quite touristic and can be packed in Summer (mid-July to mid-August), with associated traffic jams, price hikes, difficult to find accommodation and a mediocre experience overall.
There is a small airport in Nîmes (FNI IATA), mostly catering for some low-cost seasonal flights from UK. The airports in Montpellier (MPL IATA) and Marseille-Marignane (MRS IATA) are better served by regular airlines are both some 50 km from Nîmes.
A TGV line connects Paris to Lyon, the Rhône Valley, Nîmes and Montpellier. It's a 3-hour ride from Paris, and there are even some direct trains from CDG airport, Probably the best option.
One of the main motorway in France (A6/A7/A9) runs along the same route as the TGV line, from Paris to Lyon to Montpellier. An easy, and rather scenic drive, but the A7 in the Rhône Valley (South of Lyon) is almost always busy, and tends to be very crowded at peak times -- spring week-ends, holidays and most of summer. Driving times of up to 5 hours (instead of the regular 3) from Lyon to Nîmes are common in busy week-ends.
Unfortunately, like most of France outside of the main city, it is difficult to go everywhere without a car.
Local trains (TER) run a handful of lines around Nîmes. The main route goes from Avignon to Nîmes to Montpellier, running through the more densely populated part of the département in the southern plain. A line goes due North to Alès, and beyond through the Cévennes into the Massif Central, towards Mende and Clermont-Ferrand.
Although the trains are rather reliable and reasonably fast, the trains are not terribly frequent.
A network of busses, operated by the Région Occitanie (LiO), goes to most towns and villages in Gard. They are cheap, but not particularly fast, and can be ridiculously infrequent (one or two busses per day) on most lines. It is a viable option, if you plan in advance and make sure you do not miss your bus!
Like most of Western Europe, the Gard has an excellent network of roads, with well-maintained tar roads going everywhere. Some of the local roads in the garrigue or the Cévennes can be very narrow and winding; all roads except the main thoroughfares go through every village, most of them having been built before the advent of motorcars. Traffic can be heavy in Summer. So in general, take your time, relax and enjoy the scenery. Do not expect an average above 60 km per hour on any given trip outside of motorways, probably less than that.
Villages, towns and cities can be tricky to negotiate with a big car: they mostly have narrow winding streets. If possible, avoid the core portions, park your car on the outskirt of town or on the main square (more often than not, there will be some parking available on the "place de l'Eglise" or, in larger places, on the "place du Marché", or places going by similar names) and walk. Many places have a weekly market - trying to drive into town on a market day is going to be time consuming and frustrating, parking on a market day may be close to impossible especially in the more popular spots (Uzès, Anduze...).
The Southerners have the reputation of being terrible drivers. Whether they are more aggressive or reckless than the average French driver remains to be seen - there is certainly a tendency to blame the neighbor. People from Northern France are convinced that Southerners are crazy, drivers in Monpellier roll their eyes in dismay when they see a car with a Gard licence plate, and people from Nîmes take it as granted that Alès drivers are insane...
Hiking, paragliding, kayaking and canoeing are practiced in this departement. Hiking and paragliding particularly in Cevennes. Kayaking in Gard river is an original way to see the Le Pont du Gard. Cèze river is a quiet river ideal for family trip.
During summer, one of the most popular pastimes for tourists and locals alike is spending the day "à la rivière" (at the river). Most rivers have beautiful swimming holes and small pebble beaches, often nice rocks or bridges from which the local kids love to jump in the water. There are simply too many such spots to offer a full list. Ask your hosts, or simply look around: if you are on a road that follows a river and see several cars parked on the side in the middle of nowhere, it is most certainly because there is a swimming hole there. Some can be quite popular, and some are real gems. Access to the river is commonly tricky (climbing down steep slopes / bushes), very often on public land and if not almost always tolerated by landlords, unless explicitly stated otherwise ("accès interdit").
French food with a Mediterranean twist.
You want to try olives and products made of olive (tapenade); in fact it would be a rare meal in Southern France that does not include olives in some form.The local cultivar is the picholine (green), originally from here; you will commonly find tanche (black), often sold as "olive de Nyons". Olive stalls on the market will typically carry an amazing range, easily 10 or 20 different kinds...
Goat cheese (Pélardon).
A range of pastry ("viennoiserie"), like most France; a local specialty is "fougasse". Depending where you are exactly, a fougasse can be different things. The one from Aigues-Morte is a sort of brioche, flavored with orange lower water. In the garrigues region, it will be made of a pastry similar to croissant, but filled with bits of bacon or, traditionally, pork fat ("grattons").
Fruits, especially in summer : melon, peaches, apricots, etc.
Although the see is close, this is not really seafood territory: historically most of the coast of Languedoc was swampy and infected with mosquitoes, with very few harbors. Fish can be found, but is neither particularly good nor cheap. As an exception, you can try brandade in Nîmes (an emulsion of salt cod crushed in olive oil and potato). Use as a spread on bread, or cooked in a potato gratin for instance.
Most towns have a weekly market, which is a wonderful opportunity to discover what the region has to offer. Get a fougasse, a handful of olives, some fresh bread and goat cheese, a small bag of fruits and head for the river for a picnic -- the true recipe for a memorable summer day!
This is a touristic place, so take normal precautions about pickpockets etc.
Realistically one of the biggest hazard is related to the heat, especially in summer. Temperatures above 35°C are not uncommon. While this is probably the reason you came here in the first place, it would not be a good idea to go hiking without a sizable amount of water, sunscreen, hat, etc. Even standing in the sun at a touristic site for the whole day is not going to be pleasant. Follow the local habits: look for shade, especially in the hot hours of the day!
If you decide to go swimming, be prepared for cold (to very cold) water, unequal bottom, rocks. Pay special attention before jumping from a rock, make sure the water is deep enough!