Termez is reached by domestic flight from Tashkent (about 1 hour 40 minutes, several flights weekly on Uzbekistan Airways) or by overnight train from Tashkent (roughly 12–14 hours). The train is a reasonable option if you enjoy long overnight journeys and want to watch the landscape change from steppe to desert.
The city sits in a restricted border zone due to its proximity to Afghanistan, and you must register your passport at your accommodation — a requirement that is enforced more strictly here than in the rest of Uzbekistan. Some archaeological sites near the border require an additional access permit, which your guide or hotel can arrange.