There you are, cruising along the crowded highway from Tel Aviv airport towards Jerusalem. Suddenly, slashing its way across the barren landscape to your left, you see it: a great, grey, concrete monstrosity, dividing creamy-white Jewish settlements from shabby Arab villages.
Welcome to Israel's second wall, the seriously controversial one which non-governmental organisations and global do-gooders love to hate. The one which divides post-1967 Israel from the West Bank, and goes on to hack its way through Arab Jerusalem. Here the wall does not separate Arab from Jew. It separates West Bank Arabs from Arabs in areas annexed (illegally, so the UN says) by victorious Israel when it redrew the city boundaries.
As a political journalist I know and hate walls. I wrote about the Berlin Wall. I walked many miles of (UK government approved) brick and concrete barriers which are still needed in Belfast to stop Republican and Unionist extremists from bombing each other's communities, more than a decade after the Good Friday "peace agreement". I have covered Cyprus since 1974 when Turkey seized the north of the island, and I have yet to come to terms with the hideous breeze block walls which disfigure medieval Nicosia.
For sheer nastiness though, I have to say, as an unswerving friend of Israel, the wall that Israel built is up there with the worst of the contemporary variety.
So the question I wanted to answer on my latest trip to Israel was: "Is this wall necessary?"
You can tell a lot about your Israeli friends from how the language they use. If they talk of the "peace wall", they are off somewhere to the right of Binyamin Netanyahu. If they use that bland official euphemism, the "separation barrier", they are probably government spin doctors. If their chilling label of choice is the "apartheid" or "segregation wall", then your friends may well be the sort of people referred to as "self-hating" Jews.
Not surprisingly, it is easy to hear the case for the wall - it was built, most people believe, to stop bombers crossing from the West Bank to unleash murder and mayhem in Jerusalem. Since its construction was completed in 2006, the number of suicide bombings and other atrocities has dropped to near zero. Ergo the wall must be a success (although that is a view perhaps more difficult to sustain after last month's appalling bus station bombing in Jerusalem). Which is why I asked radical activist Jeff Halper, an American anthropologist who made aliyah 40 years ago, and now runs the militant Israeli Committee Against House Demolitions, to give me his organisation's bitterly critical tour of the wall. He argues that it is not about security, but about making life so unpleasant for the Arabs of East Jerusalem that they give up, cross into the West Bank and never return.
I told Halper that some British Jews thought it a disgrace that groups like his - which works with Palestinians to organise passive resistance to Israeli policy - take money from foreign sources, Jewish and non-Jewish. "We are constantly told that Jews are a light unto the nations, and that Israelis somehow represent all Jews. If you make such claims, you invite the world to judge you," was his reply.
Veteran Israeli political journalist and translator, Dan Gillon, joined me on my trip.
It is only a short drive from the Western Wall, where we met up with Halper, to its modern counterpart. Pulling up against the wall, I see that the structure is huge. Block after block of solid concrete, 28 feet high. Twice the height of the old Berlin Wall, and topped off with barbed wire, security cameras and electronic warning devices. A bit over the top, all that barbed wire, I suggest. Halper grins. "Not so. Little Arab kids used to climb the wall somehow, straddle it and ridicule the Israeli police."
There is graffiti everywhere. Cartoons, poems and the occasional four letter word. Half-hearted efforts to whitewash out the insults have been made, but it is clear the authorities have pretty much given up. We parked alongside the unimaginative and not entirely convincing "Scotland Supports Palestine". Where the wall passes the grand residences of the international representatives of various Churches, the PR-conscious powers-that-be have faced the harsh concrete with elegant tiles.
Only two crossings have been built in this part of the wall. The Olive Crossing is miles from anywhere, seriously big and built to last; akin to a flashy airport terminal, all chrome and glass and high-tech security. Tens of thousands of Palestinians who live on one side of the wall work on the other. Most have friends or relatives on the other. They go through procedures which can be as complex and time-consuming as those (rightly) imposed by Israeli security before you can board an El Al flight from Heathrow. Journeys which use to take 10 minutes now take an hour or more. The new Shuafat Terminal, not yet complete, is even bigger and more off-putting. It comes with an official notice: "Please keep the terminal clean. Have a good day". It is nice to know the authorities care.
Having viewed the wall up close, Dan Gillon's conclusions were distressing. "I have known Jerusalem since before Israel existed," he told me. "I welcomed its liberation in 1967 and rejoiced that we allowed Arabs and Jews to mingle freely. I am a liberal but I fully understand the security arguments made by those who built the wall. Even so, its construction does not make me feel more secure. Instead, I fear it signals the inevitability of yet another war before too long."
As for me, I am marginally less pessimistic. I recall the poem, Mending Wall, in which the idealistic Robert Frost describes a quarrel with his neighbour in rural New England. "Something there is that doesn't love a wall," Frost begins.
The poem ends with his tough old neighbour strengthening the wall which divides their properties. "Good fences make good neighbours," the realist says. My heart may be with Frost. But my head is with the realist. Good fences do make good neighbours. For me, Israel's wall is a necessary evil. Just don't ask me to love it.