Where is the best places to travel in hot summer season?

In the hot summer season, I'd like to go some place where they are "not-too-hot" and "not-too-cold" to stay. I'm living in Ireland now, and usually the temp here from 20-28 in the hot summer season which is quite cooler than other hot countries but still gives good warm feeling. Do you know any other great places to travel in the hot summer season?