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Novotel Bangkok Suvarnabhumi Airport is the closest hotel to the airport you can find. Don't be worried about the traffic it's just in front of the airport, at only 5 minutes drive or walk (thought the underground tunnel).
There is a free 24-hour shuttle service which is running every 15 minutes from and to the airport. You can reach it at the airport on the second level, exit 4.

Link to Google Map

This 4-star hotel is not the cheapest place you can find in this area, but if you have an early flight, this is the place where you won't have to wake up hours before to be sure to be on time.

It's a big building with a very big lobby, 612 rooms and Suites, 7 restaurants and bars, a Spa, a swimming pool, a tropical garden, a business lounge, 2 receptions (one in the Business Center for VIP guests and Executive rooms), a tailor, an art gallery and a souvenir shop (over-priced).

Rooms are spacious and very quiet. The only problem can be the size of the building. If your room is located on the opposite side of the lifts you will have a lot of walking if you go often "up and down" to the different areas of the hotel.
Some of the rooms are surrounding the tropical garden while the others are surrounding the swimming pool.

The atmosphere inside the hotel is very quiet and a bit "cold", with lots of clean and polished marbles and orchids on every floor. This is a high-standing hotel. Like in a lot of big hotel chains, the staff is just doing their job and that's all. You won't get the warm welcome you can get in smaller hotels or resorts.

Inside the hotel you have the choice between 7 restaurants and bars:
- Sala Thai: Thai cuisine
- Golden Village: Cantonese cuisine
- Kinsen: Japanese cuisine
- Le Gourmet: French pastries
- The Square: International cuisine
- Atrium Terrace: cocktails and snacks
- Splash Pool Bar: at the pool, cocktails, and snacks

There are also a Spa, a spacious Fitness Center with a lot of equipment, a very nice outdoor swimming pool and a beautiful tropical garden which is not very easy to find, you may even not notice it.
The Spa is proposing different types of massages and treatments. In the Fitness Center, there is equipment for fitness but also for work-out. Bikes, treadmills, cross-trainers, machines to train isolated muscles, barbells, benches but also propose Thai boxing courses. They also supply towels.
In the lockers room, there are a Jacuzzi and a sauna (men are women are separated).

The swimming pool is on the same floor level as the Fitness Center and Spa. Like it's more often in the shadow than in the sun, I found the water a bit "cold". But once inside you get used to it very fast.
There are a few sunbeds, tables, and chairs all around. You get free clean towels. The Splash pool bar is proposing all kinds of drinks, as well as cocktails and small snacks.
There are lots of plants and beautiful orchids all around.

Even if it's in front of the international airport, the garden or the pool are very quiet, you don't even notice the planes which are landing or taking-off. The reason is that they are surrounded by a tall building. The downside is that the pool gets under the shadow early.
You can even see the air traffic control tower from the pool.

Inside the rooms you don't listen to any noise at all, there is excellent sound insulation. 
Rooms are very spacious and they all have a bathtub and a shower in their bathroom, individual and programmable a/c, LCD TV with international channels.
I would recommend the Executive Rooms, they are a bit more expensive but you get extra privileges like a King-size bed (or twin beds depending on your choice), an espresso machine, extra beauty products in the bathroom, the daily newspaper, complimentary fruits and chocolates (in your room only when you arrive), free daily small bottles of water (also in your room), fast check-in and out with a VIP reception (in the Business Center), complimentary coffee and tea with cakes served in the afternoon in the Business Center, complimentary drinks (alcoholic or not) with warm and cold snacks every evening which can easily replace your evening meal and all of that for free and as much as you want!

Finally the tropical garden.
It's not very easy to notice it except if your bedroom is surrounding it. It's on the opposite side of the swimming pool. From the lobby, take the stairs which are on the left side of the reception (reception facing you), and follow the small signs.
This garden is full of plants and flowers with small water ponds. It's a very good place if you want to relax, meditate or read a book. It's normally empty, at least all the time I've been there I've never seen anybody else.

Availability and Prices at Novotel Bangkok Suvarnabhumi Airport!