Martin is a very friendly and helpful host. My girlfriend and I arrived in the evening. In the room, we found a map and Martin showed us on the map some nice places where to eat (f.e. "cocos & curry" or "bite me"). He also gave us some advice about parking the car and the very strict controles if you have not got a ticket :-) We could always knock if we had a question. It is a warm and cosy place.
For big and heavy suitcases, you should keep in mind the stairs :-) but it was fine for us.

The appartment is quite quiet and sunny and the Piet Hein straat very nice. We had breakfast at the "Crunch" and there was f.e. a shop called Collectura, a funny mixture of comic and pin up (!) collectibles. The Panorama Mesdag Museum is "around the corner". Take an audio guide!
The city center with the grote Kerk or the Museum Mauritshuis (where you find the Mädchen mit dem Perlenohrring) is within a 20 - 25 minutes walk. And you should try the pommes frits in 't kleinste Winkeltche in the city center. We went to China town and had a very good lunch there. If we did not want to go out, there was a kitchen and a fridge. Try the Albert Heijn fresh spicy sushi.

To discover the city from a different angle, we recommend a 2-hour "Hofjes Tour", in Dutch language, to be booked at the Tourist information.
Finally, Scheveningen/ the beach is not far, either by bus or about 45 minutes walk. But we liked the kijkduin even better.
All in all, a very pleasant stay. Martin and his place are highly recommendable. Dank je wel, Martin!