Lielvārde is a little town along the Daugava River about an hour drive southeast of Riga. They have a reconstruction of a wooden castle similar to the one in Tērvete. There's no need to choose a favorite between them since they're both fun to explore. There's a castle ruin on the other side of town in the manor complex. The nice park grounds around it with huge carved poles are a great place to stroll around. Finally, there's a named waterfall listed on their tourist board. If you're not interested in the castles then skip to the end to see that amazing wonder.
