Yes English. No we did not book in advance.

As many have said, 1.5 hours worked for us, too. We are looking forward to going back :)

There are signs asking that no photos are taken inside the castle. You can purchase books and postcards from the the shop showing the interior I think.

You can purchase on the day; plan to take the funicular railway to the castle from the town centre, get there early. When getting the funicular railway, your get a combination for the ride and the castle.

The Heidelberg Tun is 7 metres high, 8.5m wide, holds 220,000 litres of wine and has a dance floor built on top of it!

Volgens mij is de Entree €.9,= per persoon

Not a Viking cruise but I did the Rhine cruise with Riviera Travel - can I be of help?

ハイデルベルク中央駅でてすぐの観光案内所でハイデルベルクガードを買ってください。 ハイデルベルク城までのケーブルカー往復と お城の入場料、 期間中の公共交通機関乗り放題で1日券、2日券があります。多分1日券大人で15ユーロでした。

Ik vrees dat niet alles met de rolstoel te bekijken is. Wegens de middeleeuwse structuur van het kasteel bevat het nogal wat trappen. Laat je echter niet weerhouden en bezoek zeker de buitenzijde en mooie binnenplaats.

You don't need to book anything in advance. Just make sure you make yourself familiar with opening times before getting there. The castle and funicular are open every day, but most museums are closed on Mondays. We were there last November on the first Monday of the Christmas Market when most attractions were shut and the ones that were open shut at 4 and we still had a great time. I assume in September there will be longer opening hours and the river cruise may still be running.