It is marvelous trekking spot, and which you can easily execute. Please keep the place clean, do not litter. Keep a small map on your device or small hardcopy of it, so you can ease your trip. Kalsubai is around 180 km from Pune and around 150–160 km from Mumbai. We had left from Pune in late night on bikes. We reached at Bari, the base village, within 5 hours. Drive carefully coz it's very hard mountainous road. It is a very nice village, and it'll be very great if you reach there early morning bcoz the scenario of this area is very beautiful to keep in our eyes forever. At village Bari, when you reach in morning, you will get very early hospitality service at many houses over there. If you want little new change in cleaning your teeth, try to demand their local “misari”, it is local tooth powder, which gives you a new freshness. Try a pinch of it becoz it'll coz some dizziness. (Note- try it at your own risk). You will get regular breakfast (poha), and tea. And take some parcel with you if you want. The village has parking space near Maruti mandir. Take a good amount of water with you from village itself.
Then you can start to trek, try to make it early in the morning, coz when sun is on your head you will get fussy. So start early. It'll take mere 1:30 to 2 hours to climb. You can see various scenarios, mountains around Kalsubai, view of Bhandardara dam will give you heavenly pleasure.
I am recommending anyone going there to stay at least for 2–3 days. The whole area around is very beautiful to capture in your memories. You can find various tent service providers over there. Various resorts are also available.
Darjeeling is more like 'chota' Shimla - it's crowded. There are some good eateries to try and some shopping that you can do as tourist. This is if you are planning to travel. If you plan to trek, you have multiple, stunning treks to explore.