Subject: Re: Paris Hotel in August
Hi, Lucy... We have not stayed at the Hotel Observatoire Luxembourg, but the reviews on Trip Advisor are good, and it's located near the Luxembourg RER station, though not as close to the Seine as you'd like. According to one of the reviews on Trip Advisor, the train from the airport takes you right to the hotel.

http://www.observatoirehotel.com/

Best, Sandy in Illinois