Accommodation and Tours in Ulanbaatar Mongolia
I strongly advise to make a reservation well in advance if you want to stay in a budget kind of accommodation such as a hostel in Ulanbaatar, especially during peak season in August. I made the experience that a lot of travelers were rejected in several different places I stayed. It might not be funny if you are arriving at night and the door is slammed in to your face, as pickpocketing and bag slashing is a growing concern and alcoholism is a serious problem too. You might not be able to find a reasonable priced hotel if you are rejected and urgently need to find a place to stay somewhere around.
I do not recommend day trips to Gorkhi-Terelj National Park. You might find yourself four out of six hours in the traffic chaos of the city center. It ist better to stay one night in the park even if the Ger Camps usually do not provide electricity or bathroom facilities. If you are just spending a few day in Ulanbataar, it would be a good Idea to book a three day two night trip to Kharkorin, make as stopover at the sand dunes between Khustain NP and Kharkorin and take the Gorkhi-Terelj NP as an additional day. Friends of mine were very happy doing this. Most of the hotels and budget places in Ulanbataar are able to help you managing to find a tour operator. Be aware, the old Russian jeeps might exude an adventurous atmosphere, but in our case they were the wrong choice (cold & windy, technical problems).