Besides the famous Pashiputhinath and Swayambhunath, there are many other temples in Kathmandu Valley area. Explore the small streets and lanes. Many of temples found in this area are very old and you can admire the intricate or colorful design on the exterior.
Most of the people, pilgrims and tourists, are to be found along the Bagamati River or in the temples on the western side of the river. Steps lead up from the eastern side of the river, too, and by going up you get into another warren of little temples that are much quieter and more serene. Lots of monkeys will keep you company as you wander about.
You may find many terrace fields and green valleys once you come out of Kathmandu towards Pokhara by road. There are forests, rivers and mountains everywhere. People live in harmony with nature.
Walking through the many connecting alleyways in the "Old City" you come across some amazing little area's and actually feel like you are making a discovery around every corner.
Dont miss the beautiful buildings in Nepal, very many of them are decorated with amazing woodcarvings and i can say that i never saw 2 similar ones!
At Durbar Square many holy men will ask you for money to take a picture. A true holy men won't ask you for it.
Many small villages, like Bungamati and Kokhana, are worth visiting. You can walk from one to another, it's only one hour or so. Interesting sights and friendly people will welcome you, for sure...!
My suggestin to stay on the beaten track in this country as its bloody cold and its easy to get lost and die from the exteeme cold.
When in Kathmandu, you should explore the city to have a feel on the actual daily life. Although the city is dusty, lively and chaotic, it is quite safe to walk around.