We need a basic, how long are you going for, this looks like a 6 week holiday to me and even so some rushing may be required.

Autumn (i think is fall right) is getting well over by the time you are into this so think chilly even so the shear spread of your trip means weather will be all over the place so Dubrovnik may be 24C while Dublin 10C and raining.

So give us a clue, how long?

Back up buddy - you are all over the map here. Unless you are on a passport stamping and photo gathering exercise you would need to seriously reconsider this itinerary.

I count 13 counties in 2 months, which would probably be 3-4 days on the ground in each country. To think of the amount of air miles you will clock up here, not to mention the cost to yourself and the amount of lost time you wil incur on planes, then it would be my idea of hell.

If you like architecture then Spain would be a must anyway.

In 2 months why not pick out 3 countries you would like to see in detail and pick them.

Good thing you're starting off from Switzerland it can only get warmer from there. I'm related to Singaporeans, you feel the cold. I'll be in Italy and France around the same time. This is what I'm bringing, 2 travel shirts long sleeve for warm weather, 2 skivvys for cold weather ,1 very light merino jumper and 1 thick woollen cardigan which can be worn over several layers if needed. Also a light gortex packable parka, 2 long travel pants that can be rolled up in hot weather and a light black skirt for going out.

I will be going for around 2-2.5 months. depending on whether how many I can do. There are some countries, I will only want to be in one city. E.g. Austria and Portugal.

You may only want to be in one city in a country but this is still extra time in transit, crossing borders and potentially visa issues. Regardless, this is not a good way to travel in my opinion, and I've done a bit over the years. It makes no sense to me.

Also, look at your outer points on a map - Dublin, Stockholm, Istanbul and Lisbon - that is one big area. Too big for two months at any rate.

For someone living in Europe, going to Vienna on a city break makes sense. But for you who has 2 months+, I see no point in going to Austria just to see Vienna. When I backpacked around SE Asia, the idea of going to Cambodia to see only Phnom Phenh made no sense. Likewise, why would a backpacker go to Ecuador just to see Quito. And so on.

Absorb a country properly and do the majority of your travel overland where you will meet locals, save yourself money. Do you really want to return to Singapore and show your friends a bunch of pictures of downtown Barcelona, Madrid, Paris London, Athens etc. Get off the beaten track, explore a bit.

I may be rambling a bit here and I wish you all the best but I think your plan is crazy!!

I suggest you get a copy of the excellent Lonely Planet 'Europe on a Shoestring' travel guide, last revised Oct 2011, in addition to advice on this forum.
Also ask the same question on Lonely Planet Thorntree Western Europe forum, geared to young backpackers.

ok. Will review the places to visit. Thanks for all the advices! =)

I think you need to look close to specifics. For example in Greece you mention as spots of interest Athens and Melissani. Melissani is a lake inside a cave on Cephalonia island, about 2 kms outside Sami town and interior of cave is accessible only on licensed boats. I am 95% sure than cave is not accessible off season, but even if it is, Cephalonia doesn't seem to fit in easily along with Athens and possibly you'll have to backtrack back to Athens to then move onto next destination.