Semarang is the capital of central Java and doesn't really offer the traveller that much other than an overnight stop, as it is the route for buses heading eastwards towards Surabaya and Bali and south towards Yogyakarta.
The accommodation in Semarang is more geared towards the Indonesian business traveller than the tourist, however you can find reasonably priced places on Jalan Iman Bonjol.
If you spend a day here then you should make your way to the vibrant Chinese quarter, which is supposed to be the largest on Java. This area is surely the liveliest area of Semarang and you won't be disappointed with the photo opportunities you will encounter. The market is a criss cross of small alleyways that will fool your senses into thinking you have stepped back in time.
If you need to escape the city, just head 5 kms south to Gedung Batu. It is here that you will find the most important Chinese temple on Java. The temple is built from a deep red stone and is dedicated to Zhenghe, a fiftheenth century envoy of the Ming Dynasty. It comprises of four shrines and is built around a cave where it is believed that Zhenghe meditated for the first time in 1406.