Originally Posted by
dulciusexasperis
As is often the case, without background info, any answer is as good as any other in terms of throwing a dart at a dartboard. If circumstances warrant and you want to buy 50E then the advise to just go to the closest makes sense. If you want to buy 500E then the best advice would be to not do that at all as you would be better off buying on arrival in a Euro using country.
The OP did not ask for advice about what would be the best strategy to obtain euros but instead asked a precise question. Why not answer the question which was asked, rather than berating the OP for not asking the question that you think would be a better question? Maybe the OP has his/her reasons for asking that question. For instance, if the OP only has cards that have a +/- 3% loading on exchange rates (like many credit and debit card do), it may make more sense to change in London, where there are plenty of bureaux de change with rather good exchange rates, which would not necessarily be the case at his/her destination in Euroland.
Somebody else has mentioned
https://travelmoney.moneysavingexpert.com/, which is an excellent resource that will enable the OP to find out whether there is a bureau de change with a good exchange rate at a location which is convenient for him or her and whether it would be worth his/her while or not to travel further to get a better rate.
Getting cash before travel is of course not the only solution but let the OP be judge of that .