Candi Penataran
This is the largest ancient Hindu temple in the East Java region. It dates from the early Majapahit period and texts clearly indicate that it was of considerable importance. Prime Minister Gajah Mada visited here 4 times for example. It is a large complex with 3 courtyards and in many ways strongly recalls a modern day Balinese temple. There are a number of interesting relics including a substantial wall relief depicting the Ramayana.
Gunung Kelud
A semi-active volcano whose eruption in 1919 killed over 5,000. It is still active and sent a pylon of smoke 2.5 km into the air in 2007. The nature at the top is amazing and the trip up is maybe even more beautiful. At the top there are also warm, sulfurous hot springs one can bathe in.
Sukarno's grave
This fits it well with a visit to Candi Penataran as it is on the same road mid-way between Blitar and the temple. Indonesia's first president and independence hero Sukarno has undergone a huge rehabilitation in the eyes of Indonesians since the downfall of the Soeharto dictatorship and his grave here is flamboyantly decorated and worth a quick stop after seeing Penataran.
Tambakrejo Beach
This is an extensive and attractive 10 km stretch of white sand beach that is more often than not virtually deserted. It is not safe for swimming though.
Sukarno Museum
This museum and library is housed in the property where Sukarno lived as a young boy. Full of Sukarno memorabilia, papers, photographs etc and very much worth a visit in conjunction with a trip to the grave site.