I hope you find something interesting to add in form of billboard or else.
PREHISTORY: Dinosaurs
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The Iberian Peninsula formed around 310 million years ago and the oldest dinosaur record is from 152 million years ago. There are a few museums devoted to dinosarus among other interesting sites with fossilized dino footsteps:
Dinópolis, a dinosaur theme park in Teruel
https://www.dinopolis.com
Museums
MUJA in Asturias region (near Gijón)
https://www.google.com/maps/place/Museo ... -5.2740996
MUPA in Castilla-La Mancha (Cuenca)
https://www.google.com/maps/place/Museo ... -2.1287667
Dinosaur Museum in Salas de los Infantes (Burgos, Castilla y León)
http://www.fundaciondinosaurioscyl.com/es/museo/?
There's also a Dinopark (as in the Czech Republic) in Algar, near Alicante.
PREHISTORY: Ancient men
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Approximately 800 000 years ago, the first humans entered the Iberian peninsula. The most famous sites are:
Atapuerca (Burgos, Castilla y León). The most important of them all.
Altamira caves (Cantabria). Modern men in Spain wall painting (as old as 35000 years)
Antequera Dolmens (Málaga, Andalucía), from Neolithic and Calcolithic.

Los Millares (Almería, Andalucía) one of the earliest cities and cultures/civilizations from Iberia (and Europe!). From 3200-2200 bC (Copper Age).

Scientist found in Almería interesting paintings and symbols on many caves (prior to Los Millares), these are INDALOS, and they are very proud of them:
Other sites:
-Las Cogotas (Ávila, Castilla y León)
-San Fornés (Mallorca, Islas Baleares)
-Cancho Roano (Badajoz, Extremadura)
-Numancia, Celtiberian town (Soria, Castilla y León)
What is the KINGDOM OF TARTESSOS? The Greek reported a kingdom in what today would be the southwest of the Iberian peninsula, apparently they had quite influence and traded a lot with Eastern Mediterranean civilisations. There's not much written evidence that support that, but it's fairly accepted that it was the first political entity of the region. By then there were Celts in the North-West of the peninsula that overrun ancient European peoples, and Iberian in the South and East. Central Iberia was a place where Iberian and Celts would fight and melt creating new languages and cultures (Celtiberians).
ANCIENT HISTORY
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With the arrival of Greek, Phoenitians and, later on, Carthaginian settlers, History begins. Iberian people received eastern influences that let them develop a writing system (3, actually). Phoenitians gave name to Spain (the land of rabbits) and Greeks to the peninsula. The most important IBERIAN ART is:
La Dama de Elche (Elche, Alicante, Comunitat Valenciana), but it's in a Museum in Madrid.
La Dama de Baza (Baza, Granada, Andalucía)
After the 1st Punic War of the 3rd century bC between Carthaginians and Romans) Carthage started to colonize southern and eastern Spain until Sagunto, where the limit of the Roman influence was established. Things start to speed up now, they found many actual cities on what would have been native Iberian settlements on the coast: Cádiz, Málaga, Cartagena, Alicante... the rest is war and destruction for Carthage after a nice Italian incursion transporting African elephants through the Pyrinees and the Alps accompanied with many Iberian & Celtic mercenaries.
Fun fact: they say Cartagena was founded over some Iberian settlement (Mastia, but again, not much evidence to support that thesis), it were the Carthaginians who founded and named the city after their metropolis: CARTHAGE founds NEW CARTHAGE because their harbours were similar, Carthage at the same time used to be a colony of the ill-fated phoenitian metropolis that didn't stand a chance against all those Minor Asian empires that conquered the area in succesive waves. Well, it happens that Carthage means NEW CITY, therefore, QART-HADAST (Cartagena) means something like NEW NEW CITY in Phoenitian. Later iterations were CARTAGO NOVA (roman), CARTAGO SPARTARIA (under Byzantinian Empire), CARTAYANNAT AL-HALFA (or just Cartayanna) during the Islamic period untill 1245 when it was baptised as Cartagena.
Now back to our History: IMPORTANT ROMAN CITIES:
-MÉRIDA: terribly beautiful, there's a circus, a theater, part of an aqueduct and an amphitheater.
-TARRAGONA, just gorgeous, probably the most important Roman city of Hispania.
The Romans created provinces (Tarraconensis (North), Lusitania (West) and Baetica (South), then Carthaginesis (southeast), Gallaecia (Galicia) and Ballearica (Balearic Islands). They ended up being overrun by many Germanic tribes in Iberia by the end of the 5th century, the Visigoths were the dominant one and they established their capital in Toledo.
MIDDLE AGES
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The Visigoth didn't last long, they asked North African tribes to get involved in their inner quarrels and eventually got conquered by them under the name of Islam.
IMPORTANT ISLAMIC CITIES
-CÓRDOBA (Medina Azahara, the Roman Ruins and the HUGE mosque).
-GRANADA (Alhambra and the Generalife under Sierra Nevada mountains)
Some visigoth retreated North and created the earliest medieval kingdoms and dynasties that eventually led to the foundations of Spain (and Portugal as a result). The first was Asturias, then it was renamed as León, then Castilla, then Navarra. There Francs established a March in the Northeast that conformed the catalan counties. Later on there was another kingdom, Aragón. Then, Portugal got independent from León. The rest is war between the Christian kingdoms when they weren't fighting the islamic caliphate under holy war. Long story short: by 1492 the Christians had conquered it all and continued to conquer overseas, joined kingdoms under marriage and conquered or annexed the rest (Navarra in 1520 and Portugal from 1580 to 1640).
IMPORTANT MEDIEVAL FIGURES:
El CID CAMPEADOR (in Burgos)
DON QUIJOTE DE LA MANCHA, not an historical character, but very important in Castilla-La Mancha, especially Toledo
MODERN TIMES
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Museo Nacional del Prado in Madrid, one of the most important of the world.
Museo Guggenheim in Bilbao
Museo Reina Sofía & Museo Thyssen in Madrid
Museo Dalí (Figueres, Girona, Catalonia)
Ciudad de las Artes y las Ciencias (Valencia)
Modernist Architecture from Barcelona (Gaudí)