The point of the Ole Sereni is that it is very close to the airport and therefore is used by airline crews or those with short stopovers.
For those it is a good choice. It is situated is outside of the CBD in a quiet location about 10 minutes drive from the airport. The public area are very nice with a large comfortable bar and massive terrace overlooking scrub land. The y say you can see wildlife from there but I did not.
The room was less impressive, a very hard bed and sparse furnishings. The sink was in the room and the toilet and shower (no bath) in a curious glass cubicle. Still an effort is made by the hotel, the towels are all presented with a hotel wrap around ribbon, a chocolate is on the bed, free wifi (not that quick), mini bar and decent bath amenities.
The breakfast was nice and started very early (5.30am).
The main problem for me was a bad night's sleep thanks to the rock hard beds and quite a lot of noise.
There are much better hotels in Nairobi (the Serena is a proper 5 star) but for a layover between flights the Ole Sereni is fine.
