Kourou is small town (20 000 inhabitans) in the sea side of French Guiana. In the town is nothing nice to see, beaches around are nice but you can't swim because of mug.
Town might be know because Guiana Space Centre which lies nearby. You can visit this place for free. The centre is open for visitors even in rocket launch days (cca one time per month). But you should book in advance. Normally just book one day ahead.
Nice place to visit is also old prison facility on Devil's Island.