I work in an international school but in the UK. I've worked in international schools since I finished my NQT year, so have a lot of friends who have 'done the circuit'. They have all had a mixture of experiences - some amazing schools in amazing places, some awful schools in amazing places, some awful schools in awful places. Top line is do your research thoroughly on the school and the location and go through any contract you get offered with a fine tooth comb. You often have to sign a two year contract and schools can make it hard for you to leave earlier if you decide it's not for you.
My colleagues unanimously say that Spain is the worst place to teach abroad, by the way. The salaries are the lowest in Europe due to the popularity of the location, and my colleagues who have taught in Spain have said you really struggle to make ends meet. We're talking UPS teachers taking home 1500 euros a month after tax. SERIOUSLY low pay. The behaviour of the children and the whole ethos around the value of education is also not great, apparently, and I haven't met anyone who has genuinely enjoyed teaching in Spain. All left after their two year contracts were up. So be warned - Spain is not the best location.
Friends of mine have had fabulous experiences teaching in Mexico, Argentina, Costa Rica and Peru, though. Would you consider Latin America? Now that could really be an adventure!
In order to have real flexibility of employment, having International baccalaureate (IB) experience is a big bonus. I've only taught IB for years now and can barely remember the British curriculum. The IB for me is the reason why I have deliberately chosen to teach in international schools in the UK -the curriculum is concept and enquiry based and allows teachers a huge amount of creativity and freedom. There are no formal exams until the final year of school, so you don't have to waste your time teaching to tests throughout the middle years of secondary school. Teaching in IB schools abroad and teaching in British schools abroad would be very different experiences - the British schools tend to cater for locals as opposed to the expat communities, who tend to go to the IB schools as the curriculum is more portable for international moves. If you're interested in making international teaching a new career for you, I'd recommend going on an IB training course so that you can apply to more possible vacancies.
Good luck with your adventure! I am getting to the point now where I might be ready to jump ship and am excited to see what vacancies come up when schools start to recruit. As a heads up, the International recruitment circuit is earlier than the UK one - jobs will start coming up from October and most vacancies are filled by January.