It's been raining all day today.

The mountains are more beautiful, and the waterfalls are more spectacular than yesterday.

The backdownside is that we have to walk in the rain.

The worst thing iwas that my shoes aregot soaked.

Luckily, the hostel owner hasd a shoe dryer, and he lendst it to me.

What's a shoe dryer!!!? :)

It's been raining all day today.

加個「been」強調從早上到目前全天都在下雨了

The mountains are more beautiful, and the waterfalls are morend waterfalls are even more beautiful and spectacular than yesterday.

加個「even」表達昨天的山川已經美麗，今天更美麗，這樣好聽
你寫的還可以但是這樣更好聽，把同一樣的句子結構連續寫聽得比較奇怪，可以放在一起

The backdownside is that we have to walk in the rain.

Luckily, the hostel owner has a shoe dryer, and that he lends ito me / he will lend to me.

He lends to me = 你已經待在hostel一段時間，使用過了烘乾機而會繼續使用這台烘乾機
He will lend to me = 你知道hostel的主人有一台烘乾機，你還沒有使用過但是你期待他會讓你使用

I hope I'll have a dry pair of dry shoes tomorrow morning.

你寫的在語法的方面還可以
但是它有「新雙的干鞋」的含義因為「一雙」強調了
把dry放在前面強調dry，你目前有的一雙鞋子會變干的含義更清楚

RThe rain or it’s raining

The backsidinconvenience is that we have to walk in the rain.

Luckily, the hostel owner has a shoe dryer, and he lendst it to me.

The backside is that we have to walk in the rain.

"We have to walk on the backside in the rain." Do you mean something like this? I actually don't know what exactly a "backside" is.

It's been raining all day today.

The mountains are more beautiful, and the waterfalls are more spectacular than yesterday.

The backdownside is that we have to walk in the rain.

Even though we have umbrellas, our clothes are still got wet.

The worst thing is that my shoes are soaked.

Luckily, the hostel owner has a shoe dryer, and he lendst it to me.

It's been raining all day today.

it's raining (now)
it's been raining (it started raining earlier, it's still raining now)

The backdownside is that we have to walk in the rain.

"the downside"

Even though we have umbrellas, our clothes are still got wet.

Luckily, the hostel owner has a shoe dryer, and he lends it to met me borrow it.