Not sure where to go - 4 days in March

The weather can be quite different, depending on where you are in Spain / Portugal, with the south being appreciably warmer than the north. Switzerland and Austria will still be cold, with daytime highs in the single digits (celcius) and a good likelihood of rain or snow. Of course the mountain elevations will have more snow than the valleys. Cloudy days are more likely than not. Scotland will be cold and damp, with single digit daytime highs, and one of the rainier months.

That time of year, I'd be heading to a major city with a large variety of indoor things to explore. Edinburgh and Glasgow, Lisbon, any of the major cities in Spain, Vienna, and perhaps Zurich. Just dress appropriately for the weather.

etexan.ashley,
With four full days, just one city. My choice would be Vienna, or Porto, Portugal, or Sevilla/ Cordova Spain. All would give you four full days, but relaxing and not rushed.

Early March try Barcelona, Sevilla, Cordoba or Lisbon.

If it's after 20 March consider Amsterdam for the flowers.

https://keukenhof.nl/en/

Fly Turkish Air to get to Europe and lay over in Istanbul for 4 days.

You didn't say WHERE the wedding is taking place! I suggest that you visit places close to that place. 4 days is not much, so don't plan a lot of travel.

The cities I'd be looking at most closely would be Vienna, Paris, Madrid, London and Edinburgh, likely in that order.

Thank you, everyone, for these suggestions and notes!
The wedding is in the UK, but we don't want to limit ourselves too much by that location since quick flights are available from the places we're considering. We plan to fly in Sunday and fly out Friday morning, giving us 4 full explore days to play with.

@CJean - I know... I started with a wide range of options (locationally and weather-wise!). Great note to look for a variety of indoor things to explore.

@KGC - Unfortunately, we will be there too early in March. I used to live in NL, so I hoped to line up our trip with tulip season, but it's looking to be too difficult to logistically. Good suggestion, though.

I think we've narrowed to Lisbon, Madrid, and Vienna based on suggestions and preferences. Thank you!!

Train to France or Brussels