From Cadiz, up the Guadalquivir River to Seville. It's a navigable river, and small cruise ships go up there, so should be no draught problems.
No idea where to moor though - last time I was there, didn't see any obvious visitor moorings or facilities. Food in Seville is wonderful, just wander round the bars eating Tapas to your hearts content
You can anchor virtually anywhere on the river Guadalquiver, only ensuring you keep clear of the channel. The lower stretches are not particularly attractive though, so it's probably worth doing what we did, and push up a fair way with the tide in the first instance. The Donana National Park forms the left bank for many miles, but when we were there, had suffered from some ghastly river pollution spillage that had destroyed much of the wildlife. This was well on the way to recovery though, so we were told, so by now should be back to normal.
There are (were) two marinas near Seville. A small, very cheap one, built for some major sporting games, and the one belonging to the Seville Yacht Club, which is much nearer the centre of the city.
We stayed at the smaller one, which was very quiet, extremely friendly and astonishingly cheap. A 50p bus ride took you right to the city centre, passing major superstores etc on the way - ideal for stocking up cheaply. Seville is a fantastic place in our view, and we would love to have stayed longer than the 10 days or so we were there. So yes, do take the time to visit, I'm sure you will not be disappionted.