Nothing is quite so impressive in Van as the Van Castle, which dominates the view of the city. About 3km west of the city centre, it's a wonderful place to come for a picnic.
Just past the spot where the minibus drops you, on the northern side of the rock, is a modern mosque and the tomb of Abdurrahman Gazi, a Muslim holy man. It's frequently visited by pilgrims including infertile women who are thought to be helped by coming here. Further on, at the northwestern corner, you'll reach the ticket office, then the car park, where there are toilets and a tea garden.
A stairway from the car park leads up the rock. Once you've reached the summit, the old city reveals itself like Pandora's box. Over towards the southern face of the rock you'll see an iron gateway blocking off a lengthy cuneiform inscription. This recounts the high points of King Argishti I's reign (786-764 BC). There are also several rock-cut funeral chambers, including King Argishti's.
Continue up to the top of the rock, where you can see the fortifications, including the Sardur Burcu (Sardur Tower, 840-830 BC) with several cuneiform inscriptions in Assyrian praising the Urartian King Sardur I.
If you look down to the south of the rock, you'll see a flat space broken up by the grass-covered foundations of numerous buildings. This was the site of Tushpa, an Urartian city that flourished almost 3000 years ago, although the foundations you see are those of the old city of Van, destroyed during the upheavals of WWI. Time is well spent walking around the base of the rock afterwards and inspecting these ruins, preferably taking someone to guide you for safety and avoid potential hassles from kids. Of the Seljuk Ulu Cami only a broken brick minaret remains, but the Hüsrev Paşa Külliyesi, dating back to 1567, has been restored and you may be able to get inside to see the fine brick dome and fragmentary murals. If not, you can still inspect the delicate kümbet (tomb) attached. The nearby Kaya Çelebi Camii (1662) has a similarly striped minaret but is still in use and likely to be locked except at prayer times.