Distance: 3.3 km (2.5 DOC hours) - Unmarked route, clear
Altitude: 1655m to 1825m. Gain: 507m. Loss: 523m . Gradient: 18 deg (Moderate-hard)
Skills: Prolonged scrambles (4/7)

Unmarked route, clear (7/9)
Unmarked route, follows obvious geography (river, spur, trail, etc)

Secondary, unmapped (4/5)
Route not on maps, an alternative recognised access to hut or along range / catchment

Moderate-hard (difficulty: 4/5)
Continuous moderate climbs

Unknown (difficulty: 0/5)
Not specified

Prolonged scrambles (difficulty: 4/7)
Scramble, frequently on exposed ridges, spurs, faces

None (difficulty: 1/6)
No unbridged river crossings

Unknown (difficulty: 0/7)
Not specified

(merging notes from route by Millera)

From D’Urville Pass begins the long sidle around the head of the D’Urville valley to Thompson Pass. This sidle is best done at 1,700m elevation for most of it. However, careful route choice is required near Thompson Pass, as it is simply not possible to reach the scree/chute leading to Thompson Pass at this elevation, due to a long and wide crevice in the rock from about 1,800m elevation to 1,600m elevation, and possibly even further down to the valley – this is not shown on the 1:50,000 topo maps, nor are the large number of bluffs around here, nor the roughness of the ridge. It is particularly frustrating to encounter this crevice, as I did, as the scree/chute to Thompson Pass is tantalisingly close, at just over 100m away. This sub-section describes the descent from D’Urville Pass, the sidle at 1,700m, and my route to Thompson Pass.
The first part of the route is reasonably straight forward, descending scree to a fairly flat section with a small tarn. While it seems better to head south from D’Urville Pass, since that went toward the destination, this should be avoided, as it leads above bluffs. Instead stay north on the scree and continue to descend the scree, to the left of the rocks and bluffs as you descend. This is straight forward, with some careful clambering over a section of small vertical bluffs when almost at 1,700m elevation.
Most of the sidle is best done at 1,700m elevation, as described in other trip reports. Once on the flat section, at 1,700m, travel is straightforward, although over boulders at times. It then reaches steep boulder and scree slopes, which required careful footing and slow travel. Other trip reports describe beginning an ascent from about NNW of peak 1,964 to 1,770m. I continued further at 1,700m, then began an ascent to 1,800m – the sidle across the scree and boulders from higher looked more difficult, and the ascent to 1,800m after this was straightforward. I found a ledge, at this point, and began travelling towards Thompson Pass. However, I then encountered a very steep and rocky section, which I was not prepared to attempt to climb. Moreover, the ridge was significantly rougher than indicated by other trip reports and by the topo map, and while they talked about heading for the ridge, this did not seem wise. Therefore, I descended again to nearly 1,700m elevation where I found a grassy ledge that was an easy walk towards Thompson Pass. There were some small trickles of water in places, which could be useful near the end of the long traverse. In hindsight I wonder if it would have been better to only ascend to 1,740m and take what appears to be a ledge to these grassy ledges.
After walking along the grassy ledge I encountered the deep vertical crevice in rock, with Thompson Pass frustratingly close over the other side of it. Walking uphill beside this was reasonably easy on tussock, alpine plants and rocks. It eventually ended allowing travel northwest towards Thompson Pass. Soon after I encountered the bluff covered ridge line, and a narrow chute leading to the north-west side of the ridge above Thompson Pass. While the chute was narrow and steep, it was possible to scramble up it, including through a patch of snow, and no worse than some parts of the Waiau side of the Waiau Pass. After ascending this chute the ridge opens out to narrow grass ledges between steep rocky outcrops (Figure 16a). It was easy enough to pick a route between these, zigzagging down to Thompson Pass (Figure 17a).
As I stood on the pass, I saw to the north a group of five kea fly from the Waiau Valley side over the ridge and into the D’Urville Valley, calling out as they flew.
The walk to Lake Thompson down the Waiau side of Thompson Pass is a straightforward descent of 100m then contouring around a grassy rise from the ridgeline to the lake itself, taking just 20 minutes.

Note: Described in the reverse direction to your journey

From the Pass we climbed to the east (there is an obvious grassy ramp back from the middle of the pass) and picked our way through the rocks (occasionally spotting cairns) to descend to a bit of a ledge, initially at the 1800m contour and then at 1700m. Rather than traverse below the final bluffs, we climbed a steep shallow gut – a very easy approach to D’Urville Pass.

You need good visibility for this route.