I have a UK-issued NPPL(A) with microlight rating, can I fly my own aircraft to Spain on this?
The NPPL is a UK only license and is not recognized by other countries, however there is a letter of agreement between the UK and France that you can fly there provided you have a medical. There is no such agreement with Spain, however you can contact their version of the CAA and maybe get permission, I'm not sure what hoops you would need to jump through on that.
A chap on the Microlight Forum helpfully phoned AESA to ask:
The Spanish Agency (AESA) [...] confirm that to fly a microlight in Spain you need a Class 2 or a LAPL medical certificate. The LAPL certificate is the least they accept, and must be issued by an aeromedical examiner.
The CAA document Which type of Medical Certificate or Declaration can I use for my licence? is also kind of useful in working out what the options are, if not actually giving the answer for individual countries.