Brussels Travel Forum

15-Jul leaving in the morning from Cielo's to Cologne, Germany The Hauptbahnhof (MAIN TRAIN STATION)
15-Jul All Day using Eurail Pass Cologne, GERMANY to Brussels, BELGIUM Thalys to Brussels-Midi via EURAIL PASS
16-Jul arriving in London from Brussels, BELGIUM to London, ENGLAND via EUROSTAR TICKETS
17-Jul All Day in London All Day in London
18-Jul flight to Dublin, Ireland from London, ENGLAND to Dublin, IRELAND Airlines and Flight Number
19-Jul All Day in Dublin All Day in Dublin
20-Jul flying in to Paris France from Dublin, IRELAND to Paris, FRANCE Airlines and Flight Number
21-Jul All Day in Paris
22-Jul Eurail Select Pass from Paris FRANCE to Nice, FRANCE Is there a train from Paris, France to Nice, France?
23-Jul All Day in Nice All Day in Nice
24-Jul Eurail Select Pass from Nice, France to Barcelona, SPAIN via EURAIL
25-Jul All Day in Barcelona All Day in Spain

Well, if you are happy to spend only a day in cities which most people allow at least 3 or 4 to explore (and most of which need several weeks to explore fully) then I suppose your itinerary is ok and your train selection too.

http://www.bahn.de/international/view/en/index.shtml

will give you train times and details, in English, for almost all European trains.

You will, of course, be spending most of your time travelling: on the train, at the airports, getting to and from the railway stations and the airports.

I strongly suggest you cut down on the number of places you visit (miss out Nice, for example) and allow at least 2 full days to explore each one. It would also make more sense to fly from Paris to Barcelona, imo.

Have you booked you flights yet? If you are using budget airlines you should do so as soon as possible: there are no last minute cheap fares, and fares rise the neareer you get to departure. Check hold baggage limits (20kg for most, 15kg for Ryanair) and remember that if you are a minute or two late for check-in you will miss your flight with no refund. www.whichbudget.com lists European budget carriers and their routes.

You should also book your Eurostar tickets if you have not already done so. The booking 'window' is open 120 days in advance of travel and the cheaper fares soon sell-out. The official booking site is www.eurostar.com (you will not find cheaper tickets elsewhere).

Brussels is the wrong forum to ask about trains from Paris to Nice, but of course they exist, they take between 5-6 and 10 hours, and if you insist on going there, you might do best to take the overnight one that leaves Austerlitz at 22:25 and arrives at Nice-Ville at 08:47.
I presume you realise that with a Eurail pass you still have to pay for reservations on Thalys (Cologne-Brussels) and Eurostar (Brussels-London).
As for your time frame for each city, anything is possible but while you can just about see the highlights (Grand' Place, Galeries St. Hubert..) in Brussels, you will have to be highly selective in London and Paris, in fact it hardly seems worth your going there for one day only. Also, Nice is not on the way to Barcelona, it takes 13 hours from one to the other, with several changes. I agree with the previous recommendation, cut out Nice, and go direct to Barcelona (which takes 13-19 hrs from Paris; or go overnight from Paris to Toulouse and then travel on from there).
Btw you can't travel to Spain - or anywhere else - "via Eurail": train operator will be French Railways (SNCF) and/or Spanish Railways (RENFE).

If this is really only a ten day trip I'd limit myself to just two cities. And forget the Eurail pass. It's a ripoff that is absolutely not needed.

Entirely agree about the Eurail pass.