As the highest point in Great Britain, and the highest of the Munros (Scottish mountains over 3,000 ft), Ben Nevis is a hugely popular hill to climb. It is 1,344 metres (4,409 ft) above sea level, and the start of the walk really begins right by the sea so you'll walk every foot of those 4,409. The Ben, as it is popularly known, is readily accessible via a man-made path which zig zags up its south westerly face, whilst the foreboding rock face on the north west of the mountain is strictly for experienced mountaineers only.
Despite the path up the mountain being referred to as the "Tourist Route" - don't let its inauspicious name fool you. Climbing Ben Nevis should be regarded as a serious undertaking, regardless of the time of year and dozens of injuries and even deaths occur on the mountain due to ill-preparedness. Whilst Ben Nevis is nowhere near the hardest Munro to climb, it is among the more challenging due to the sheer relentlessness of the climb, and in particular the descent which can take its toll on ankles and joints. Figure on taking 6-9 hours to make the round trip to the summit; bear this in mind during early spring and late summer when darkness can creep in surprisingly quickly.
The key points to remember are as follows:
Ben Nevis is on the outskirts of Fort William, which is reachable by road from Glasgow (105 miles) or Inverness (65 miles) via the A82. Fort William is served by the West Highland Railway; ScotRail  run a number of daily trains from Glasgow and Mallaig, in addition to an overnight rail service from London six nights a week.
The two usual approaches are from Achintee Farm or Glen Nevis. Both are over a mile out of Fort William, and of the two, the Achintee route is less steep to begin with (they merge pretty soon) and has some free parking spaces (this fills up early in the height of summer), while at Glen Nevis visitor centre there is more parking but you have to pay.
The usual route is the Tourist Route, aka The Pony Track. This runs from the end of the lane at Achintee Farm, though there is an access route from Glen Nevis Youth Hostel, and heads up in a series of zig-zags to the summit on a broad, obvious path. It's a relentless slog, well trod and eroded by tens of thousands of people every year, though path repair work is currently underway. The path heads steadily uphill, a couple of small zig-zags, then curves left at a cleft in the hill before levelling out at what is known as the Halfway Lochan. (It's slightly before half-way but who cares, it's a morale boost.) Then are the zig-zags proper, a series of eight switchbacks in the path, then a final straight up the final slopes of the hill.
The "interesting" route is to ascend the outlying hill Carn Mor Dearg, and traverse the arrete to Ben Nevis proper, but this one is strictly for equipped, experienced mountaineers.
At this altitude the temperature is considerably lower than in the valley where you start out, plus you need to factor in for some wind chill, meaning that you need warm clothing. Even at the height of summer the temperature at the summit is barely above freezing and is usually covered by snow all year round.
You're unlikely to get lost until you reach the summit plateau. A direct walk across the summit to the cairn would send you tumbling down a gully, which becomes a hazard when filled with corniced snow which may look safe to walk upon. Overshoot the summit or lose your bearings and you may fall off the mountain, such as via the dramatically named Five Fingered Gully. These issues don't sound too much of a problem until you realise that even in summer the summit is fogbound more than half the time.
Temporary cairns (that is piles of stones) are often erected to mark the "safe" route to the summit, but DON'T rely on them as they are a subject of derision by experienced hillwalkers who regard them as both an eyesore and a "cheat sheet" - and are therefore often knocked down.
There is a small survival shelter on the summit, known as the Snoopy Hut, built on the ruins of the old observatory to avoid it becoming snowbound.
Many visitors arrive as part of a Three Peaks Challenge event, particularly in the middle of summer when there's plenty of daylight. This involves climbing the highest mountains in Scotland, England and Wales, and can cause chaos. Charity organisers are asked to follow a code of practice, which limits group sizes, access hours, timed challenges, etc. The biggest risk if you're a participant is breaking your ankle if you're running downhill - which also helps erode the paths in a scenic area!
There's a distinct lack of toilets on the route, or even handy pathside bushes. On descent your first toilets are at the Ben Nevis Inn, at Achintee, but they're only open during pub hours. At Glen Nevis visitor centre there are also toilets. The only slightly private spot during the walk is by the Halfway Lochan, 100yds down a spur path to the north from the route, where a large rock affords you a little privacy. But it gets pretty gross back there.
RAF Air-Sea Rescue offer free rides in a big yellow helicopter, but it's considered bad form to call upon them.
Fort William is at the foot of the hill and is the obvious base for food, drink, accommodation, equipment shopping and onward travel.