Probably about ~35-40 apartments in Barcelona. Going out to Spanish rural areas, you could probably buy ~4-6 abandoned villages with that, you'll get multiple houses, municipal buildings and whatever administrative stuff they had too.
But then you'd have to keep stealing more gold bars for the upkeep, and who has time for that?
But then you'd have to keep stealing more gold bars for the upkeep, and who has time for that?