Takatsuma
Getting there:
From Nagano station, take the 70 or 71 Highland Express bus (timetable) to Togakushi Campsite. The bus leaves from the Zenkoji exit of the station on the opposite side of the road (map). The bus takes around an hour to reach the campsite.
The campsite itself is attached to a large ranch. It gets busy in the summer months over the school vacation, but is quite large enough to support several hundred tents. If it is school vacation season, prepare for a noisy night of fireworks (but you can seek your revenge when you wake at 4am..!).
It is probably not necessary to make a reservation in advance. They have freestanding tents and some log cabins which presumably can be rented out. There is also a useful live webcam if you are interested in conditions at the bottom.
The route:
From the campsite, you walk north-west through the ranch with the mountain ridge rising impressively in front of you. The route is very straightforward and well marked. You shortly pass into the forest which begins at the bottom of the climb and after 45 minutes or so enter the shallow gorge which the river has carved in the mountainside.
The climb from here to the ridge takes just over an hour. The trail passes over several areas of sliprock, most of which have fixed chains. There is a small spring half way up with potable water, just above the fudo waterfalls.

The top of the climb to the ridge is marked with an small emergency hut, at which you turn right and continue on up to Gojizo-dake. There is a trail from Gojizo, unmarked on the map, which apparently returns to the ranch.
From here you will be getting your first views of the cone of Takatsuma, as well as great views back down the Togakushi valley. The trails swings round to the west, and eventually to the bottom of Takatsuma proper. The approach turns steep at this point, and there is a risk of rockfall (especially if there are others above you). it’s a relatively short, steep climb up to the boulder strewn top of the mountain.

At the top, you will pass by a statue of Kwannon (Guan Yin) on the right, and after a hundred meters or so of climbing among the boulders to the peak itself. On a clear day you should be able to see the Sea of Japan to the north, the north alps, central alps, south alps and Mount Fuji, as well as the remains of many ancient volcanoes in the area.
The route down is the reverse of the route up, although the trail from Gojizo may be an option. On the way down be aware that the steep trail and wet conditions caused by the stream which flows most of the year make for slippery going.
If you have time on the way back, Togakushi shrine is worth a visit - the bus back to the station passes by (and in summer months will pick up many tourists at this stop), or is walkable in an hour from the campsite.
Summary:
Togakushi is a beautiful area with some very impressive scenery. The climb up to Takatsuma can be done in 7-8 hours in good weather, and is a fun route but not too taxing. In winter when the mountain is largely inaccessible the area can be snow-shoed right up to Togakushi Okusha shrine, and there are plenty of pensions in the area to stay at during the cold months. Don’t miss the soba noodles - the area is famous (deservedly) for them!