Here's the postcard with present continuous underlined and past simple circled:
Hi Caitlin,
This is my second day in Wales. We arrived last Saturday. The journey by coach from London was very long! We're staying at a campsite near a lake in Snowdonia National Park. It's very beautiful here and the weather is fantastic - warm and sunny.
Yesterday we trekked up a mountain and then climbed up a cliff. Then we abseiled down the cliff! It was really fun. Today we explored the countryside near the lake and then cycled to a town near here.
Tomorrow we're kayaking on the lake, and maybe we're going caving too. Isn't it wow!
Say hello to Jimmy. Wish you were here!
Bye for now!
Joe